Color plots

Graphsize 600,600
fastgraphics
clg
for pic = 1 to 2
for x= 1 to 600
for y= 1 to 600
# try different formulae for color using coordenates x and y
if pic = 1 then color ((x-300)^2+(y-300)^2)*3
if pic = 2 then color 300*abs((x-300)/(y-300))
plot x,y
next y
refresh
next x
next pic