Sky seems to turn darker REALLY FAST while getting deeper in the water.

Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report ([minecraft|http://hopper.minecraft.net/help/finding-minecraft-data-folder]/crash-reports/crash-<DATE>-client.txt) here.

Attached.Please don't say it's the render distance or the clouds,I tried in many ways,worked the same.

Did you take a look at the crash report?

Yes, and I couldn't see anything odd about it. I'll ask another mod who knows more about graphics cards and drivers to take a look at it, though.

Cannot confirm with 14w25b.
The sky darkens a little bit, but not so excessive like in your screenshots.

No, did try.
But 14w25a is outdated, can you confirm this with 14w25b ? If so, please attach screenshots.

OpenGL: AMD Radeon HD 5450 (Microsoft Corporation - WDDM v1.2) GL version 4.2.12417 Compatibility Profile Context 13.150.102.0, ATI Technologies Inc.

Your graphics driver is outdated. Please install AMD Catalyst 14.4: http://support.amd.com/en-us/download/desktop?os=Windows+7+-+32#amd-catalyst-packages

Anyway, I will verify this bug as soon as possible.
I've updated the driver.

Hm, confirmed on 14w27a.Now the sky is again very dark like in the screenshots.

Is still still an issue in 14w30c ? If so, please attach screenshots with debug screen enabled.