extensions/notebook-renderers/src/color.ts/_parseHexDigit
			function _parseHexDigit(charCode: CharCode): number {
				switch (charCode) {
					case CharCode.Digit0: return 0;
					case CharCode.Digit1: return 1;
					case CharCode.Digit2: return 2;
					case CharCode.Digit3: return 3;
					case CharCode.Digit4: return 4;
					case CharCode.Digit5: return 5;
					case CharCode.Digit6: return 6;
					case CharCode.Digit7: return 7;
					case CharCode.Digit8: return 8;
					case CharCode.Digit9: return 9;
					case CharCode.a: return 10;
					case CharCode.A: return 10;
					case CharCode.b: return 11;
					case CharCode.B: return 11;
					case CharCode.c: return 12;
					case CharCode.C: return 12;
					case CharCode.d: return 13;
					case CharCode.D: return 13;
					case CharCode.e: return 14;
					case CharCode.E: return 14;
					case CharCode.f: return 15;
					case CharCode.F: return 15;
				}
				return 0;
			}