tui-cs/Terminal.Gui · error · ColorParseException

Value was not composed entirely of decimal digits.

Error message

Value was not composed entirely of decimal digits.

What it means

Thrown inside ParseRgbaFormat when an rgb()/rgba() string contains 4 comma-separated values but the alpha (4th) component is not composed entirely of ASCII decimal digits. It is a ColorParseException whose BadValue is the alpha substring and BadValueName is "A". This pinpoints the alpha channel as the offending component.

Source

Thrown at Terminal.Gui/Drawing/Color/Color.Formatting.cs:390

                        return new Color (int.Parse (rSpan), int.Parse (gSpan), int.Parse (bSpan));
                    }
                case 4:
                    {
                        // rgba(r,g,b,a)
                        ParseRgbValues (
                                        in valuesSubstring,
                                        in valueRanges,
                                        in originalString,
                                        out ReadOnlySpan<char> rSpan,
                                        out ReadOnlySpan<char> gSpan,
                                        out ReadOnlySpan<char> bSpan
                                       );
                        ReadOnlySpan<char> aSpan = valuesSubstring [valueRanges [3]];

                        if (!aSpan.IsAllAsciiDigits ())
                        {
                            throw new ColorParseException (
                                                           in originalString,
                                                           "Value was not composed entirely of decimal digits.",
                                                           in aSpan,
                                                           nameof (A)
                                                          );
                        }

                        return new Color (int.Parse (rSpan), int.Parse (gSpan), int.Parse (bSpan), int.Parse (aSpan));
                    }
                default:
                    throw new ColorParseException (
                                                   in originalString,
                                                   $"Wrong number of values. Expected 3 or 4 decimal integers. Got {rangeCount}.",
                                                   in originalString
                                                  );
            }

            [Pure]

View on GitHub (pinned to 2e47b11478)

Solutions

1. Ensure the alpha value is a non-negative integer string of digits only.
2. If your source alpha is a 0..1 float, convert it to 0..255 integer first.
3. Use Color.TryParse to catch the malformed rgba input.

Example fix

// before
Color c = Color.Parse($"rgb({r},{g},{b},{alphaFloat})");

// after
int alphaByte = (int)Math.Round(alphaFloat * 255);
Color c = Color.Parse($"rgb({r},{g},{b},{alphaByte})");

string a = alphaSpan.ToString();
if (!a.AsSpan().IsAllAsciiDigits()) return fallbackColor;

static bool IsValidAlphaComponent(string s) => s.AsSpan().IsAllAsciiDigits() && int.Parse(s) is >= 0 and <= 255;

try { c = Color.Parse($"rgb({r},{g},{b},{a})"); } catch (ColorParseException ex) { /* ex.BadValueName == "A" */ c = fallback; }

When it happens

Trigger: Passing "rgb(10,20,30,-5)" (negative sign is not a digit), "rgb(10,20,30,0x10)" (hex), or "rgb(10,20,30,2.5)" (decimal point). Only unsigned integer decimals are accepted.

Common situations: Passing alpha as a float (common in CSS where alpha is 0..1), negative values, or hex notation inside an rgb() string.

Related errors

• Color hex string {hexString} was not in a supported format
• Wrong number of values. Expected 3 or 4 decimal integers. Go
• The text provided consisted of only whitespace characters.
• Text was too short to be any possible supported format.
• Text did not match any expected format.

AI-assisted analysis of tui-cs/Terminal.Gui@2e47b11478 (2026-08-13). Data as JSON: /api/errors/f4af8f82482379d1. Report an issue: GitHub.