Photoshop :: Simulating Snow On A Tree

1. I'm not very satisfied with the snow in the trees, i've tried many filters and finally used "replace color" on the greenish parts of the trees with luminosity at 100%. I've compared with real snow covered trees and they are completely white, i guess that i should somehow "paint" them but i don't know a lot about how to achieve a realistic snow effect with the brushes (without degrading too much the original trees either...)

2. The icy sea is taken from another photo i found on the web (probably antarctica). It seemed to blend nicely when i was working on the retouching but when i opened the project 2 days later i thought that the colors of the two photos didn't blend *that* nicely Is there a "scientific" way to harmonize the colors of two photos, so that they can fit well together? (i'm prepared to hear that there's no recipe for that!)

(seemed to me that the blending of colors is top priority but perhaps something else is jumping even more at your eyes).