This Code is a convert from this Stackoverflow thread.
B4X:
Private Sub isColorDark(color As Int) As Boolean
Dim darkness As Int = 1 - (0.299 * GetARGB(color)(1) + 0.587 * GetARGB(color)(2) + 0.114 * GetARGB(color)(3))/255
If darkness <= 0.5 Then
Return False 'It's a light color
Else
Return True 'It's a dark color
End If
End Sub
Sub GetARGB(Color As Int) As Int()
Dim res(4) As Int
res(0) = Bit.UnsignedShiftRight(Bit.And(Color, 0xff000000), 24)
res(1) = Bit.UnsignedShiftRight(Bit.And(Color, 0xff0000), 16)
res(2) = Bit.UnsignedShiftRight(Bit.And(Color, 0xff00), 8)
res(3) = Bit.And(Color, 0xff)
Return res
End Sub
B4X:
public boolean isColorDark(int color){
double darkness = 1-(0.299*Color.red(color) + 0.587*Color.green(color) + 0.114*Color.blue(color))/255;
if(darkness<0.5){
return false; // It's a light color
}else{
return true; // It's a dark color
}
}