//Back color
button1->BackColor = Color::Black;
//or
string StringWithColorCode = "Black";
button1->BackColor = System::Drawing::ColorTranslator::FromHtml(StringWithColorCode);

//Fore Color
button1->ForeColor = Color::White;
//or
string StringWithColorCode = "White";
button1->ForeColor = System::Drawing::ColorTranslator::FromHtml(StringWithColorCode);