Macro define_color

macro_rules! define_color {
    ($name:ident, $r:expr, $g:expr, $b:expr, $doc:expr) => { ... };
    ($name:ident, $r:expr, $g:expr, $b:expr, $a: expr, $doc:expr) => { ... };
}

Defines and names a color based on its R, G, B, A values.