The C64 only has one 16 colour palette and that is fix (but look a bit different on every C64 because of the transistors)
Noone knows the proper RGB values and there are not any, since it is a YUV colourmodel. Many people have eyeballed them quite well, others failed miserably (whoever made the CCS64 palette is blind), Pepto actually used some measureing device and some hardcore calculation to arrive at his palette. So in that respect it's the most accurate in terms of saturation and value ratio between the colours. On a TV you can just adjust your brightness and saturation tho to change them but the relative values and saturation of course stays.
About the sprites, no that is not possible.
On the C64 you can have 8 hardware sprites which are 24x21 pixels big. They can be doubled in x, y or both (which actually is a hack) and you can have 8 per scanline with multiplexing them (also software hack)
All sprites on screen have 2 colours in common and 1 colour can be chosen from the first 8 colours of the C64 palette.
So that would be colours 0-7.
0: black, 1: white, 2: red, 3: cyan,
4: purple, 5: dark green, 6: dark blue, 7: yellow,
8: orange, 9: dark brown, 10: light red, 11: dark grey,
12: middle grey, 13: light green, 14: light blue, 15: light grey
And the 4th colour is of course transparency.
Hires sprites can be only 1 colour, but any of the 16.
And yes you can layer sprites, but it should not be overdone unles you only want one enemy on screen and no other sprites at all