Starting in Bitbucket 8.10.0, hex colors in markdown will have the corresponding color rendered next to it, e.g.

Some examples of valid hex colors:

#ff00FF
#8855aA34
#000
#aaA
#12345678
#987
#9876
#F0A5

(e.g. in above examples, the 8 char hex colors use an alpha value at the end).

Note that:

• Colors are not detected if they are between links or texts
• Colors need to be between \s \t \n or nothing.
• # is also used to do PR's links. If there is a collision between a PR ID and a color, the PR link will take precedence. As a workaround, colors may be re-written, e.g. #123 can be re-written as #123F and it represents exactly the same color. 
  • If a PR with the ID doesn't exist, then the hex color is rendered