SubtitleEdit/subtitleedit · error · FormatException

Hex string must be 6 (RRGGBB) or 8 (AARRGGBB) characters lon

Error message

Hex string must be 6 (RRGGBB) or 8 (AARRGGBB) characters long.

What it means

FormatException from FromHex: after stripping '#', the string length is neither 6 (RRGGBB) nor 8 (AARRGGBB). CSS-style 3-char shorthand (#FFF) and 4-char forms are rejected, and the 8-char form requires alpha FIRST (AARRGGBB), not last.

Source

Thrown at src/ui/Logic/SkColorExtensions.cs:57

        if (hex.Length == 6)
        {
            // Format: RRGGBB
            r = byte.Parse(hex.Substring(0, 2), NumberStyles.HexNumber);
            g = byte.Parse(hex.Substring(2, 2), NumberStyles.HexNumber);
            b = byte.Parse(hex.Substring(4, 2), NumberStyles.HexNumber);
        }
        else if (hex.Length == 8)
        {
            // Format: AARRGGBB
            a = byte.Parse(hex.Substring(0, 2), NumberStyles.HexNumber);
            r = byte.Parse(hex.Substring(2, 2), NumberStyles.HexNumber);
            g = byte.Parse(hex.Substring(4, 2), NumberStyles.HexNumber);
            b = byte.Parse(hex.Substring(6, 2), NumberStyles.HexNumber);
        }
        else
        {
            throw new FormatException("Hex string must be 6 (RRGGBB) or 8 (AARRGGBB) characters long.");
        }

        return new SKColor(r, g, b, a);
    }
}

View on GitHub (pinned to 17a9f07487)

Solutions

1. Expand 3-char shorthand to 6 and 4-char to 8, reordering alpha to the front if needed.
2. Validate the length is 6 or 8 (after '#') before parsing.
3. Document the expected AARRGGBB ordering at the UI/config boundary.

Example fix

// before
var c = userInput.FromHex();

// after
static SKColor FromHexSafe(string hex)
{
    hex = (hex ?? "").Trim().TrimStart('#');
    if (hex.Length == 3) hex = string.Concat(hex.Select(ch => new string(ch, 2)));
    if (hex.Length == 6) hex = "FF" + hex; // opaque alpha first -> AARRGGBB
    return hex.Length == 8 ? hex.FromHex() : SKColors.White;
}

hex = (hex ?? "").Trim().TrimStart('#');
if (hex.Length == 3) hex = string.Concat(hex.Select(c => new string(c, 2)));
if (hex.Length == 6) hex = "FF" + hex;
if (hex.Length != 8 || !hex.All("0123456789abcdefABCDEF".Contains)) throw new FormatException("Bad hex");

SKColor color;
try { color = NormalizeHex(userInput).FromHex(); }
catch (FormatException) { color = SKColors.White; logger.LogWarning("Invalid hex '{Input}', using default", userInput); }

When it happens

Trigger: '#FFF' (3-char shorthand), '#RRGGBBAA' (alpha last, but the parser expects AARRGGBB), odd-length typos, or ARGB-vs-RGBA ordering confusion.

Common situations: Pasting CSS hex into a setting that expects AARRGGBB, alpha-channel ordering mismatches, or loosely-validated user input.

Related errors

• Hex string must be 6 (RRGGBB) or 8 (AARRGGBB) characters lon
• Invalid hex string.
• Color '{colorName}' not found in SKColors.
• Invalid hex string.
• Invalid version format

AI-assisted analysis of SubtitleEdit/subtitleedit@17a9f07487 (2026-08-13). Data as JSON: /api/errors/9ca5317f3881e632. Report an issue: GitHub.