Update all icons to cyan to make it easier to spot changes

[pausan]

This change updates colors of all icons for consistency. Merge this change only if you like it and after applying my other pull request "Improve user experience in tree panel (two folder colors + tooltips)".

I don't really mind about the color, it could have been redish, but I think usually red is a hint for "something is wrong", and since it is not the case, I chosed cyan.