darthmunky said:

His skin actually looks real in ROTJ. In ROTS, it looks like he's wearing a rubber mask and has 2 yellow pennies in his eyes.

I agree. The first time I saw a picture of the ROTS makeup, I thought it could have been a fan-made mockup or a make-up test, not the final makeup for the movie ...

Darth Solo said:

The mono colouring shines up like a shiney new penny for the main part of the image (although its not really mono).

Sorry, but I think it looks like "Sky Captain ...". Stylistic, not real. Hues of grey are never perfect grey in real life, we just think of them as being that. I look out the window from where I am sitting right now, and the snowy hillside outside me has hues of blue and magenta where it is reflecting more of the blue sky than direct sunlight.

Everyone knows that snow is white, so we think of it as looking white, when no object (apart from a lamp) actually has any colour of its own - only what colours it is reflecting.

The Emperor's throne room is lit by lamps of various colours, by Endor's atmosphere and by starlight -- stars shine in all hues, not just white.

The blue tint of the set also reflects the general mood in the movie when Luke enters the throne room. Everything the Rebels are doing at this point is going bad: on Endor, in the space battle and on the Death Star.