yellow is not a primary colour

[dmcg]

Changed yellow to green, as yellow is not a primary color, so the example is wrong

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[dmcg]

I signed the CLA but nothing is happening

[MaryaBelanger]

I had to look it up, but...

Closing this, but for next time: looks like your CLA was accepted but the check that was failing was "Check if code excerpts are up to date". If you look at line 192 above the line you changed, there's a path to a corresponding dart file that needs to change along with the example in the markdown (this section in the repo readme has more info)

Thanks!