cmd/mbf: enable output colouring

This respects the de facto standards, on top of checking stderr.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/mbf/cache.go

@@ -28,6 +28,8 @@ type cache struct {
 	idle bool
 	// Unset [pkg.CSuppressInit].
 	verboseInit bool
+	// Whether to enable output colours.
+	color bool
 	// Unset [pkg.CExternShallow].
 	deep bool
 	// Loaded artifact of [rosa.QEMU].
@@ -61,6 +63,9 @@ func (cache *cache) open() (err error) {
 	if !cache.deep {
 		cache.attr.Flags |= pkg.CExternShallow
 	}
+	if cache.color {
+		cache.attr.Flags |= pkg.CColourOutput
+	}
 
 	done := make(chan struct{})
 	defer close(done)