Reagents can now mix their alpha color.

Changed water to a grey very transparent colour, so real. This also means when you water down reagents you can see them becoming very transparent, extra real!
Changed the plasma reagent's colour to look a little better.
Changed the icon of the reagent filling overlays so that they didn't mess up the colours so much.
Added a new "invisible powder" reagent which you can get by grinding the mime's crayon, this powder has no colour and has no alpha.