blotch vs color in

blotch is a noun but color in is not a noun.

Word	Noun	Adjective	Verb	Adverb
blotch	Yes	No	Yes	No
color in	No	No	Yes	No

As verbs, color in is a hypernym of blotch; that is, color in is a word with a broader meaning than blotch:

blotch: mark with spots or blotches of different color or shades of color as if stained
color in: add color to

Other hypernyms of blotch include color, colorise, colorize, colour, colour in, colourise, colourize.

blotch (noun)	color in (noun)
an irregularly shaped spot

blotch (verb)	color in (verb)
mark with spots or blotches of different color or shades of color as if stained	add color to