Light refraction within this type of 'material' follows different rules compared to the well known refraction laws water has, but they are just as coherent within that kind of structure. I think that it is because of those that syne people often perceive colours that cannot be described or picked among the colour spectrum normally available to the human eye. Furthermore, these 'different' colours have a variety of temperatures. This means that not only can a colour, in its rawest state, have a multitude of nuances from very dark to very light, but each of those picked singularly has a wide range of hot-to-cold characteristics. This aspect may or may not coincide with the equivalent characteristics of another raw colour merging with it, thus beside the mingling of the two colours themselves you stand fascinated by the new temperature of the resulting effect. The more colours mingle, the more temperatures mingle and the effects are exponential. That is why it is impossible to describe them, or riproduce them in any way. This is one of the things which frustrates me deeply, because they cannot be shared or shown and in my opinion it is a cyclopical waste of untapped beauty. Colour temperature has no ties to the environmental temperature, of course.
For the above reasons, it is quite easy for a synesthete to draw/paint proportionally and perspectively, as the 'empty space' is so easy to define. You can reproduce the chosen image by literally copying everything except that object per se, and you end up with its exact replica, of course. However, because of the refraction laws the 'empty space' has, the syne artist may well have to disregard 99% of the information received by the mingling of the colours seen and the colours usually unseen, with their temperatures and resonance. This process causes the syne artist to abandon the project before even starting, firstly because being often a perfectionist he/she already knows the end result will not be precise to its true nature, and secondly because it would be boring to create the simplified version. In two words, only synesthetes with a very low level of extra info perception could actually enjoy making static portraits.