The seventh colour is white, which is made of the six colours within it. The six colours of the chakras in the body transmute into the seventh white chakra above the head outside the body. And the seventh chakra relates to the Sun, the six colours of the other six chakras relate to the six inner planets orbiting the Sun.
That is your opinion, and you are entitled to state it.
There are other different opinions and attendant explanations or theories on the subject.
I too have my own opinions on this matter. [although it, mostly by coincidence, be similar to one or more of the previously published "alternative theories".] Have you read my thread "The Seven and the Five"? Here's a link to the most concise and understandable presentation I have to date on what I've been able so far to conceptualize and present in writing.
http://actastrology.com/viewtopic.php?f=23&t=177
It isn't too lengthy and I tried to be as succinct and concise as possible. I should let you know for your own preparation, It does also involve musical tonality.
From what I have been informed to date, Issac Newton couldn't solve the application of the spectrum to the Zodiac [or his proposal for a solution/explanation has been rejected by a substantial majority of those given the recognition, or perceived as having the qualifications, to so judge.] My explanation does solve it and with the attached explanation as to musical tonality becomes two mutually supportive and possibly mutually validating explanations. ...that is if it is truly and entirely one hundred percent correct as to what I have got presented in that link.
It fits, it solves it...but only if you believe in the purported "Seventh Ray" and alleged "lost chords" or something of that sort as to musical tonality.
I didn't set out to solve anything about any, "Seventh Ray" or the application of the colour spectrum to the Zodiac. it just worked out that way from having gotten interested in a challenge to solve the theorized application of musical tonality to the Zodiac. I just love those kind of challenges.
I also didn't start out intending to practice yoga or to become a yogi, get into Astrology or become an Astrologer. All of that just happened to become my fate along the course of my life that I took.
I also din't get into spirituality with the intention of knowing about, studying about, working with the theories of the legend of the "Ascended Masters" aka "the "White Lodge" aka "The Great White Brotherhood". and the attendant legend/myth of St. Germaine.... all that too... just worked out to be the result of the course of my life journey to date.
I was an Art Major, studied art for over 10 years, I'm quite aware of what the primary colours are both in pigment and in the light spectrum, which, as you know are different. My father was an Artist and Master Painter of the Trade, he won many an award for being the best at colour mixing/matching in competitions sponsored by the guild, the International Brotherhood of Painters.
I lost interest in pursuing a career in fine art, although I had been offered an apprenticeship position in the Scenic Artists Union at CBS Television Studios in Hollywood, in 1974, and instead became a tradesman, a journeyman painter like my father, and I completed a Union apprenticeship, local 1798 Los Angeles, Calif. and worked in the trade nearly 25 years [not counting the countless many months I worked with and for my Dad prior to that time as a lad]. I worked 13 of those years, and was briefly the Foreman painter, for the San Juan Unified School District, in Sacramento County, in care of over 84 school sites at the time, before I herniated 3 discs and was forced to retire in May of 2000.
That having been said, I think you should be able to acknowledge that I know something about colour.
As you talk of chakras, I assume you are either into yogic science, or a practitioner of one of the forms. I have been a yogi since August 1968, I am a disciple, a chela of the Bij-Mantra OM, the WORD, the LOGO, itself, as explained by Swami Sivananda in His book titled "Japa Yoga, A Comprehensive Treatise on Mantra-Sastra", Divine Life Society Press, 1978"
As being that I have no other Guru living, dis-incarnate, ascended or otherwise. I have no need for an Archetype or Avatar, Bodhisattva entity, as the Bij-mantra is all that too. My point being I have no prejudice or bias to anything other than the WORD and the LIGHT ...as the two are one and the same. I have been one with the WORD and the LIGHT, I have experienced it, and even though that was in 1968, it is the foremost memory I have and is a completely undiminished memory, as vivid and easily recalled as if it was from just a moment ago. I state as such so as not to be accused of mistaking imagination or any sort of mental imagery, induced, self produced or pre-suggested, for that of genuine experience.
I was given the name of Devananda, by some of the brethren of my fellow yogis, which I answer too when in their company and I, rather recently in 2008, became a protectorate of the Sadhan Order of Yoga of India under the guidance and protection of Sri Prabhu Ram Lal. [not to be confused with that of being a disciple, but rather one under the protection of the Order for the work, my sadhan, that I do. This is not to say that what works I have produced to date are in fact correct and of any useful purpose but rather the belief of the Swami of the Order in that I will eventually produce something of need for the spiritual betterment of Humankind [or should have, if I fail to fulfill my dharma]..I may only presently be "On the right track", or "Somewhere in the ballpark"... then again...?
I've even gone so far as to consider that I may be only a needed ruse or decoy, some sort of needed diversion. Just a fool serving, some needed purpose in some way as to, the good of the 'Great Cause'. I offered my life in service in any way or manner that God might find it to be of use, some many years ago. One never knows. I try not to take myself nearly so seriously, personally, as some want to accuse me of doing.]
The light we receive via our Sun is the same LIGHT but only in a subdued and reduced form so as it can exist in the physical universe. Scientists are puzzled as to why Sunlight is both particle and wave but this is easily fathomed when one understands it is still "THE LIGHT" and being that, it is ONE with the WORD..... light and sound, particle and wave, in unison.
So, I believe one can acknowledge that I know a bit about light, too. Although I certainly don't claim to be a, or anything of a, physicist, a 'luminescencist' or claim to be that of any title of recognized scientist in the field, relative field, or that of any other that overlaps either.
I somehow doubt that Jesus could write out a 'statistical proof' of physics demonstrating how he could walk on water or how He transmutated matter, such as changing water into wine, yet it is reported, and testimony was given, that he did so.
What I'm mostly working from a basis of is some thing one might want to label as 'Intuition', not to be confused with overtly optimistic conjecture or zealous imagination ...but that sort of 'Intuition' born out of both knowledge and of experience or a number of them, as is the case for me in regards to this subject. It does require something, as like that, of a 'leap of faith', but most of the big breakthroughs in understanding physical phenomena did require some sort of similar 'Leap', if not entirely the exact same. To 'See what lies beyond what boundaries have already been established'... and sometimes that even leads to proceeding on into what everyone else had concluded or conceded to be a 'dead end', that turns out wasn't one after all.
I was once told by someone that, I am convinced beyond doubt, knows of such things that my greatest contribution to the world will be as to something, related to or, of this subject matter and not Astrology... in relative comparison. Whether this be the right field, the correct path to pursue, or not remains for me to discover. My being so told is probably the reason, or the biggest part of it, as to why I pursue any lead in these subjects as energetically and doggedly as I do.
To produce something notable enough to be in the 'Annals of Science' for many centuries to come...and considering my lack of formal education in any of the fields of science beyond that of High School level that can only mean that it will be by genuine 'Intuition'... and possibly a certain amount of what many will ascribe to be 'Dumb Luck' but I like to think of as unexpected, unsuspected, 'Grace' from above.
19' is 84 degrees ahead of 21* 
19'. The ideal point on the matrix of the 'Mystic or Harmonic Rectangle' in my natal chart is @ 22* 
19'... to 03* 
19'...right withing an one degree orb of conj. to my natal Mars and tonights' Full Moon.
19' and 21* 
19' [the point in Libra is also part of the aforementioned 'Harmonic/Mystic Rectangle' ]in my natal chart, I've natal Neptune @ 21* 
= 
] @ 05* 
] @ 05* 
sounds like you need the well deserved vacation!