Important - a suitable forum for this question has been found: Retro-Computing Stack Exchange.
Colors are of philosophical interest for a number of reasons. One of the most important reasons is that color raises serious metaphysical issues, concerning the nature both of physical reality and of the mind. Among these issues are questions concerning whether color is part of a mind-independent reality, and what account we can give of experiences of color. These issues have been, and continue to be, inextricably linked with important epistemological and semantic issues.
- The opening paragraph from Color, on the Stanford Encyclopedia of Philosophy
This question is somewhat inter-discipline because it may have involved:
However, it does not appear to involve software architecture and design, or anything related to the software development life cycle.
The inter-discipline nature of "colorspace" has been debated before on Meta Stack Exchange: Where to ask a question about colorspace theory?.
While it appears that many questions on colorspace (including this question and the earlier question that triggered the debate on Meta) were easy to answer by pointing to a Wikipedia article, non-trivial questions about colorspace may be unable to find a uniquely suitable forum to ask on the Stack Exchange network.
The question is fully answered in the third paragraph on the Wikipedia article on YIQ. Quoted:
The YIQ system is intended to take advantage of human color-response characteristics. The eye is more sensitive to changes in the orange-blue (I) range than in the purple-green range (Q)—therefore less bandwidth is required for Q than for I. Broadcast NTSC limits I to 1.3 MHz and Q to 0.4 MHz. I and Q are frequency interleaved into the 4 MHz Y signal, which keeps the bandwidth of the overall signal down to 4.2 MHz. In YUV systems, since U and V both contain information in the orange-blue range, both components must be given the same amount of bandwidth as I to achieve similar color fidelity.
Furthermore, the design of YIQ (i.e. the engineering decisions made to exploit then-available research into the human visual system) is described in the second paragraph:
In YUV, the U and V components can be thought of as X and Y coordinates within the color space. I and Q can be thought of as a second pair of axes on the same graph, rotated 33°; therefore IQ and UV represent different coordinate systems on the same plane.