i’m glad you asked! i take it that you mean the deep blue ice found in the two glacier pictures i reblogged from tumblr user de-preciated, as well as the ice from frozen lake Baikal.
there are two reasons: the first answer is that the ice has less air in it, and the second is that water really is that blue.
in the case of glaciers, the snow and ice gets compressed so much by the weight of the glacier around it, that air is forced out of the ice. any air that remains is compressed so that it takes up minimal space. the result is that ice in the lower parts of glaciers is completely solid.
like i mentioned, water is actually blue, and that’s because water molecules absorb red and green light more readily than blue light. the blue light gets reflected back into your eyes, so that’s the color you perceive. in small amounts, like a glass of water, or a pool, that absorption is imperceptible, but the effect is more visible in greater amounts like in the ocean, or in concentrated amounts like in glacial ice. this is true in icebergs as well, because most icebergs are pieces of glaciers that have calved into the sea.
everyone and their dog, and you of course, have been taught that water is blue because it reflects the color of the sky, but that’s only true of the surface of the water. looking at this picture of a shallow sea that i found in a 7-second google search, the sky and the water aren’t even the same color. photos of the ocean reveal the same thing that glacial ice does: that water is actually blue.
unfortunately, i can’t tell you the whole story on the ice of lake baikal. i can tell you about lake baikal though. i can tell you that it’s the oldest, deepest, and most voluminous fresh water lake in the world, that it’s located in a geologically active rift zone, and that the composition of the water is nearly uniform from the surface to the floor, but i can’t come up with a reason for why the ice is so blue. i can tell you that that ice probably didn’t form on the surface; ice tends to have different arrangements depending on where and how it’s formed, and the ice at the surface of a lake forms differently than ice beneath the surface. the bluest ice found in lakes is dense, congealed ice that forms on the bottom of surface ice. you can only see it once it’s been pushed to the surface. that’s all i’ve got for you on that one.
but hey, maybe your theory is correct and lake baikal is just made out of kool aid