5     scnclr
6     b%=2:c%=3
7     pena b%
8     peno c%
10    dx% = 2: dy% = 2
30    x% = 1 : y% = 1
100   box(x%,y%;x%+10,y%+10),1
105   ask window wx%, wy%
106   b%=((b%-2) mod 12) + 3
107   pena b%
108   c%=b% 'c%=((c%-2) mod 12) + 3
109   peno c%
110   if x%<=0 then dx%=2
115   if x%+10>=wx% then dx%=-3
120   if y%<=0 then dy%=3
125   if y%+10>=wy% then dy%=-2
130   x% = x% + dx%
140   y% = y% + dy%
145   get a$
146   if a$<>"" then goto 10000
150   goto 100
10000 ask rgb 3, r%,g%,b%
10010 for i% = 15 to 3 step -1
10020 ask rgb i%, r1%,g1%,b1%
10030 rgb i% ,r%,g%,b%
10040 r%=r1% : b% = b1% : g% = g1%
10050 next
10060 goto 10000