Somebody must decide the button’s colour. Otherwise, the developer can’t complete their work.
If you don’t specify the button colour in advance, the developer must decide for you. This might be fine, or it might not.
Industry standards, style guides, accessibility best practices, user-defined themes, or the developer’s personal preference may be relevant.
Knowing which information is relevant, and when, is vital to making good decisions. Junior, inexperienced and remote developers can really struggle to get this right.
The button will be green, but there are still decisions to make. Light green, dark green, lime green, olive green. The shade of green must be decided. Otherwise, the developer can’t complete their work.
Do you understand the consequences of inappropriately made, developer-led decisions? I hope so.
Safety-critical software has very different considerations to public-facing websites, and your software development process should adequately address this somehow.
Developers should be encouraged to make the right decisions in the right circumstances while respecting appropriate limits. Not doing so can have consequences well beyond the product itself.
If you are unhappy with your development team, they may need more detailed guidance.
Clear and effective software requirements can help with this.