Some style books advise against using a colon between two phrases that are not each an independent sentence. The same applies to semicolons. The exception is when what follows begins on a new line or is a true enumeration: then the part before the colon should still be an independent sentence, but what follows is free. That is why some recommend that your colon should be replaced with a comma: the lack of reliability in bananas' drawings is not an independent sentence, but rather an apposition, which could easily be attached by a comma.
I agree that it is somewhat more elegant to stick to this rule in ordinary circumstances. However, I don't think there is consensus about this, and you may very well find style guides that disagree; at any rate, the practice of joining non-independent sentences by a colon will most probably be acceptable to the majority of readers.