Colorization - what was it's purpose?

[ReneZ]

After all, color annotations do sometimes appear in manuscripts.

I know. 
But there are not very many such cases, and this is a different question. I was (and still am) curious about the texts. I don't recall that the colour annotations seen in e.g. Vicenza MS 362 also appear in the text.
Possibly, these reflect what the outline-drawing 'artist' saw in a source MS.