item/colour.go: Change the RGBA value for black

Leather armour dying, cauldron water dying, and firework stars expect a black colour of rgba(21, 21, 33). The black colour of sign text is the exception.

server/block/sign.go

@@ -81,15 +81,15 @@ func (s Sign) BreakInfo() BreakInfo {
 // Dye dyes the Sign, changing its base colour to that of the colour passed.
 func (s Sign) Dye(pos cube.Pos, userPos mgl64.Vec3, c item.Colour) (world.Block, bool) {
 	if s.EditingFrontSide(pos, userPos) {
-		if s.Front.BaseColour == c.RGBA() {
+		if s.Front.BaseColour == c.SignRGBA() {
 			return s, false
 		}
-		s.Front.BaseColour = c.RGBA()
+		s.Front.BaseColour = c.SignRGBA()
 	} else {
-		if s.Back.BaseColour == c.RGBA() {
+		if s.Back.BaseColour == c.SignRGBA() {
 			return s, false
 		}
-		s.Back.BaseColour = c.RGBA()
+		s.Back.BaseColour = c.SignRGBA()
 	}
 	return s, true
 }

server/item/colour.go

@@ -136,8 +136,18 @@ func (c colour) RGBA() color.RGBA {
 	case 14:
 		return color.RGBA{R: 0xb0, G: 0x2e, B: 0x26, A: 0xff}
 	default:
+		return color.RGBA{R: 0x1d, G: 0x1d, B: 0x21, A: 0xff}
+	}
+}
+
+// SignRGBA returns the colour as RGBA. It is identical to the RGBA method, except for the colour black. For the colour
+// black, a value of rgba(0, 0, 0, 255) is returned rather than rgba(29, 29, 33, 255), in order to match the black sign
+// text colour found in vanilla Minecraft.
+func (c colour) SignRGBA() color.RGBA {
+	if c == 0 {
 		return color.RGBA{R: 0x00, G: 0x00, B: 0x00, A: 0xff}
 	}
+	return c.RGBA()
 }
 
 // String ...