Blending colors of shapes with their background color

Question

I have this code:

Graphics[
  {Polygon[CirclePoints[25, 4]], 
   {Yellow, Disk[{0, -15}, 1]}, 
   {Yellow, Disk[{0, 0}, 1]}, 
   {Yellow, Disk[{0, 15}, 1]}, 
   {Blue, Disk[{-15, 0}, 1]}, 
   {Blue,Disk[{-15, 15}, 1]}, 
   {Blue, Disk[{-15, -15}, 1]}, 
   {Yellow,Disk[{15, -15}, 1]}, 
   {Blue, Disk[{15, 0}, 1]}, 
   {Yellow, Disk[{15, 15}, 1]}, 
   {Red, Rectangle[{-16, -16}, {-14, 16}]}, 
   {Red, Rectangle[{-1, -16}, {1, 16}]}, 
   {Red, Rectangle[{14, -16}, {16, 16}]}}]

I am trying to figure out a simple way to make the yellow disks turn orange and the blue to turn purple when the red is over them. I looked at Blend but cannot see how that would help. I feel like there must be a simple way to do this, but have very little experience with Mathematica graphics.

Yep... just insert Opacity[0.5], before Polygon.... – David G. Stork Feb 07 '17 at 22:27 — David G. Stork, Feb 07 '17 at 22:27
Possible duplicates: (11565), (14836), (47809) – Mr.Wizard Feb 08 '17 at 02:23 — Mr.Wizard, Feb 08 '17 at 02:23

score 6 · Accepted Answer · answered Feb 08 '17 at 12:02

Not only should you introduce Opacity as suggested in the comments, you should also rearrange the order of evaluation in your graphics expression.

Graphics[
  {Polygon[CirclePoints[25, 4]],
   {Red, 
      Rectangle[{-16, -16}, {-14, 16}],
      Rectangle[{-1, -16}, {1, 16}],
      Rectangle[{14, -16}, {16, 16}]},
   {Opacity[.5],
     {Yellow,
        Disk[{0, -15}, 1], Disk[{0, 0}, 1], Disk[{0, 15}, 1], Disk[{15, -15}, 1], 
        Disk[{15, 15}, 1]},
     {Blue,
        Disk[{-15, 0}, 1], Disk[{-15, 15}, 1], Disk[{-15, -15}, 1], 
        Disk[{15, 0}, 1]}}}]

Blending colors of shapes with their background color

1 Answers1