Different colours returned per-machine

[jbrooksuk]

• PHP: 7.3
• OS: Comparing MacOS vs Ubuntu Docker Image

Given this image:

I'm getting different colours between running locally and in our testing environment.

On my Mac, the colours I get are:

• #8B849F
• #273647
• #EBB6B4
• #4E3C3E
• #987132

Whereas on our testing environment (which is a Ubuntu Docker image, running from CircleCI) I get:

• #F7ACB3
• #9AA7C7
• #B9752E
• #FDD58D
• #353A71

If we visualise these colours, we can see that they look okay. On the right, I've ordered colours to where they're most similar.

What would be the reason for seeing different colours?

[ksubileau]

I have to admit it's still a bit of a mystery to me today, and any help identifying what's going on is welcome.
I suspect this is related to rounding issues (floating point or integer casting), but I'm not sure exactly what or how to work around this.