Why are most NES player and enemy sprites so flat?

[Naniyue]

  I've been on an NES kick these past few weeks, but it's just started bothering me how flat the player and enemy sprites usually look.  The backgrounds can be rather detailed, with two or three shades of color plus black, but almost never the player/enemies.  Is this a system limitation, or an artistic choice?

Examples: 
  The chef in Panic Restaurant.
  Konami Lady and Man in Wai Wai World.
  The golem in Little Samson vs. his starting background.

[nesrocks]

System limitation. Sprites have only 3 colors.

[Naniyue]

I figured it might be such, but since I have no technical knowledge I had to ask.  Thank you!!

EDIT - Could this have been done otherwise?  Designed for more colors, or not really?

[Jorpho]

Could this have been done otherwise?  Designed for more colors, or not really?

What do you mean? Yes, if the hardware was different, it would have been capable of different things..?

[Naniyue]

If the CPU and what not was the same, just some minor hardware change to make it 3 or 4 colors?

  EDIT: And how would this affect production cost?  I know RAM and such was more expensive back then.

[Jorpho]

A lot of things were more expensive back then, yes.

If you are looking for some kind of long-winded explanation about obscure details about the NES PPU, then you can probably find one via Google.

[tobiasvl]

Hardware changes aside, it's possible to layer two sprites on top of each other to give the illusion of more colorful sprites. Mega Man does this to give two extra colors (skin and eyes) to Mega Man's face, for example.

[Jorpho]

Hardware changes aside, it's possible to layer two sprites on top of each other to give the illusion of more colorful sprites. Mega Man does this to give two extra colors (skin and eyes) to Mega Man's face, for example.

I thought Super Mario Bros 2 was the usual example of that.

Of course, the problem with doing that is that the NES can only have eight sprites per scanline without flickering – which leads to the obvious question of "why was there a limit of eight sprites per scanline", and so on.

[tygerbug]

   The background and sprite graphics on NES use four colors including transparency (or background color).

   So a sprite can have three colors, and backgrounds can have three colors plus the background color.

   In Super Mario Bros 2, three of the player characters have an extra sprite for the whites of their eyes. (These sprites are always animating, which is used in some hacks like The Thief and the Cobbler.)

   Mega Man also uses an extra sprite overlaid for more colors, and so does Ducktales. Scrooge has a "mask" to allow for eye color.

    Too many sprites onscreen slows down performance, so games would usually just use three colors for a character.

    A game can load four sprite palettes at one time, made up of three colors, and four background palettes at one time, made up of three colors and the background color.

   A sprite tile is 8x8, and these can often be set to any palette, although it's just as common that an entire character has to be one palette.

   Background color palettes generally have to be set in blocks of four tiles - 16x16. The Capcom game editor CadEditor, which supports many non-Nintendo NES games, provides a good example of this.