Something similar to this happens to me.
Periodically, whether I'm using a Texture Pack or not (which I usually am) My Textures completely freak out, and either flash from White, Green, and Default, or just become completely clear, but I can still see stuff like Chests, Ores, etc.
I'm pretty sure it has something to do with my graphics card, since I'm use a Laptop, and none of my friends experience this problem.
This also only started after I installed the 1.5 Snapshots. So I can presume it's some problem related to 1.5 not playing well with certain Graphic Cards. Hopefully this'll be fixed in 1.5.1.