harmonise vs blend in

harmonise and blend in both are verbs.

Word	Noun	Adjective	Verb	Adverb
harmonise	No	No	Yes	No
blend in	No	No	Yes	No

As verbs, blend in is a hyponym of harmonise; that is, blend in is a word with a more specific, narrower meaning than harmonise:

Other hyponyms of harmonise include coordinate, blend, go.

harmonise (verb)	blend in (verb)
bring into consonance, harmony, or accord while making music or singing	cause (something) to be mixed with (something else)
bring into consonance or accord	blend or harmonize
bring (several things) into consonance or relate harmoniously
sing or play in harmony
write a harmony for
go together