Allow custom goal colours

[m-barker]

Description

Hi,

I've often found it useful to be able to customise the goal colour when building custom environments for example, when making an environment that can have multiple goals etc.

I'm pretty confident this doesn't break or change anything (as I have just made the default "green" as it always is), but do let me know if any concerns -- thanks!

Type of change

Please delete options that are not relevant.

• [X] New feature (non-breaking change which adds functionality)

[pseudo-rnd-thoughts]

Does this work in the rendering?

[m-barker]

Does this work in the rendering?

Yeah all good! Here's a selection of the colours rendered for the empty environment: