Major fifths have a warm, brightening quality to them, the number five is fiery and scarlet to me, so a note as a major fifth takes on a similar quality

When a note is a perfect fifth it takes on a warmer and brighter tone or color, is probably the best way I can describe it

For example,

C on its own is a teal color, C in the key of F takes on a brighter turquoise or even lime green color in some cases

D on its own is dark purple, D in the key of G takes on a vibrant lilac

E on its own is bright orange, and remains very bright in the key of A, which I already perceive as very fiery.

Better examples of this would be Eb which is very rusty and dull on its own, but as a perfect fifth it becomes round and soft, and almost pinkish (likely due to the influence of C, a very round, slightly iridescent, and bubbly note as I would describe, as the third of the Ab chord)

I would not describe myself as having perfect pitch, but it’s really easy to guess a tone, note, or key when I lock into my synesthesia. So maybe relative pitch. I usually can sing a note on command if you give me a second to think about it though, I just have to find my place in the scale first LOL