I have a bundle of a red flower, blue flower, green flower, and purple flower. Are “colorful flowers” and “a colorful bundle of flowers” both acceptable?
"A colorful bunch of flowers" and "A bunch of colorful flowers" are both idiomatic.
It would usually be called a bunch of flowers rather than a bundle. Or you might call it a posy of flowers, though that seems to me a little old-fashioned. If there were more flowers - quite a lot more - it might be called a bouquet of flowers. Ngram.