docs(guide): color output controls

[crazy-max]

follow-up #1226

behavior lgtm:

but looks like the example in README of BuildKit repo is not correct:

$ BUILDKIT_COLORS="run=blue;cancel=yellow;warn=orange;error=123,12,0" docker buildx bake
WARN[0000] Could not parse BUILDKIT_COLORS component: run=blue;cancel=yellow;warn=orange;error=123,12,0  error="A valid entry must have exactly two fields"

should be run=blue:cancel=yellow:warn=orange:error=123,12,0 as correct separator but then:

$ BUILDKIT_COLORS="run=blue:cancel=yellow:warn=orange:error=123,12,0" docker buildx bake
WARN[0000] Unknown color value found in BUILDKIT_COLORS: warn=orange  error="Colors must be a name from the pre-defined list or a valid 3-part RGB value"

orange does not exist in pre-defined colors.

cc @spkane

Signed-off-by: CrazyMax crazy-max@users.noreply.github.com

[spkane]

@crazy-max Thank you for catching that. It was a last-minute change to the PR that removed the named orange color since it is not a standard 4-bit color like the other named colors. I'll also update the separator.