Compilation error when using a extern function ?

[tsalm]

Hello,

I'm on DMD 1.036.
When I'm compiling this code :

// -------------CODE-----------------------


enum ColorValues:uint
{
     AliceBlue  = 0xF0F8FFFF
    ,AntiqueWhite  = 0xF8ECD8FF
    ,Aqua  = 0x00FFFFFF
    ,Aquamarine  = 0x80FFD0FF
    ,Azure  = 0xF0FFFFFF
    ,Beige  = 0xF8F4E0FF
    ,Bisque  = 0xFFE4C8FF

     [...]


Color convertToColor(uint val)
{
    ubyte[4] colorVal = *cast(ubyte*)&val;

    return Color(    colorVal[0]
                    ,colorVal[1]
                    ,colorVal[2]
                    ,colorVal[3]
                 );
}

class DFLCalendar:Panel
{
    // Graphicals objects
    protected
    {
        // Colors default preferences :
        const Color colorPanMonth  =  
convertToColor(cast(uint)ColorValues.MidnightBlue);
        const Color colorPanDays   =  
convertToColor(cast(uint)ColorValues.White);
        const uint  heightPanMonth = 16 ;
        const uint  widthButChangeMonth = 10;
        
        [...]
// -------------END CODE-------------------

The compiler return me the error :

	tools\gui\tools\DFLCalendar.d(29): Error: cannot evaluate  
convertToColor(404254975u) at compile time

Line 29 corresponds to "const Color colorPanMonth  =  
convertToColor(cast(uint)ColorValues.MidnightBlue);"


Thanks in advance for your help,
TSalm