Ultra-SiMPLE
xc = xpixels()/2
yc = ypixels()/2
solid color (rgb(0,0,255))
solid circle (xc, yc, 250)
wait key
Do a = 0 To 255
   solid color (rgb(a,0,255-a))
   solid circle (xc, yc, 250)
   delay (10)
Loop