There's never a gray day when Amelia Gray Hamlin's around ... just sunshine, smiles and lots of curves -- and we've put together her best shots to prove it.

The model and reality star reached the quarter-century mark on Saturday ... and we know she'll be ready to hit the beach on her bday because she always looks great in a bikini.

Just check out this pic ... Amelia looks pretty in pink -- flaunting her figure in a tiny ensemble that would put Elle Woods to shame.

And -- while she may have had a cameo in "The Devil Wears Prada 2" -- this angel doesn't wear much at all, and we're all grateful for that.

Check out the gallery and wish Amelia a happy birthday!!!