COLORREF crefColor = RGB(128,0,128);

DWORD dwR = GetRValue(crefColor);
DWORD dwG = GetGValue(crefColor);
DWORD dwB = GetBValue(crefColor);

CString sValue;
sValue.Format(_T("#%02X%02X%02X"), dwR, dwG, dwB);
ASSERT(sValue == _T("#800000")); // correct