Clarification for xterm/gamma

[wernight]

The main reference table, which header is:

SOLARIZED HEX     16/8 TERMCOL  XTERM/HEX   L*A*B      RGB         HSB

Doesn't clearly state two important things:

• Which one to use or what's the difference between "HEX" and "XTERM/HEX".
• Gamma differences, like on Linux/Windows you have a lower gamma than on Mac; should those hex be adjusted depending on OS? Probably not, but answer to first point might answer this too.