[bug] backgroundColor doesn't apply globally for **some** colors

[charnould]

Prerequisites

• I am running the latest version
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed

Expected Behavior

backgroundColor should modify all canvas background-color?

Current Behavior

It doesn't seem to work as shown in the screenshot below.

For black and blue, everything is... black and blue.
However, for #151515, you can see a graph greyish background, whereas backgroundColor is indeed #151515.

Steps to Reproduce

1. Clone public repo: https://github.com/charnould/sanddance-bug-1.git
2. Open index.html with Liver-server to avoid CORS issue
3. Modify backgroundColor accordingly
4. See that current behavior is accurate --> That's the bug.

Expected result

For #151515, everything should be #151515.