TIEBitmap.GradientFillRect

procedure GradientFillRect(x1, y1, x2, y2: integer; StartValue, EndValue: Double; Direction: TIEGradientDir = gdVertical); overload;

Fills the rectangle with a specified color gradient.

Pixel Format	Values
ie1g	Specify either 0 or 1
ie8g, ie8p	Specify value between 0 and 255
ie16g	Specify value between 0 and 65535
ie24RGB, ie32RGB, ie48RGB, ieCMYK, ieCIELab	Specify TColor

// Fill image rect with a horizontal gradient from red to blue
IEBitmap.GradientFillRect( 100, 100, 200, 200, clRed, clBlue, gdHorizontal );