This appeared in 14w06a/b, and did not affect 14w05b or 1.7 or earlier.

When a creeper is about to explode, he begins an animation where he flashes and inflates. Before, the flashing was very subtle. but as of 14w06, he flashes completely white, with no texture. It looks like a white mask was applied to him without enough transparency.

A video is worth a thousand words and demonstrates how very obvious it is:

Video of how it used to look (14w05 and 1.7 and before):
http://youtu.be/KliA16AIsKk

Video of how it currently looks (14w06 and up):
http://youtu.be/wv2FWKmVgQI