How can I overlay two dense scatter plots so that I can see the outlines of each in R or Matlab?

Question

See this example

This was created in matlab by making two scatter plots indepe

Answer 1

Use the transparency capability of color descriptions. You can define a color as a sequence of four 2-byte words: muddy <- "#888888FF" . The first three pairs set the RGB colors (00 to FF); the final pair sets the transparency level.