The inspector currently show colors as decimal r,g,b values. With this change,
the hex format is used instead.
The motivation for this is that references to color typically use the hex format. One example
is the palette definitions in a color scheme. Using the inspector/cell picker to help
create and debug color themes should be more convenient after this change.
If there's a usecase for the decimal format, we could add a config option or maybe a switch
in the inspector UI.
Rather than immediately converting a color palette index into an RGB
value for a cell color, when a palette color is used track the palette
color directly in the cell state and convert to an RGB value in the
renderer.
This causes palette color changes to take effect immediately instead of
only for newly drawn cells.
