Keegan here from the Shopify Guru team.
Not a worry, while inside of Online Store > Themes > Customize theme > Colors on the Brooklyn theme you should have two main options to adjust the button color and the text within it. So if you adjust one, the other may have to be adjusted so you don't get a fully un viewable button in the process. :)
Let me know if I've totally missed your question, screenshots appreciated!
Thanks for responding! I honestly can't find, what you're showing above. I can only choose between "General" and "drawers" colors, where "general" don't have a button text option. In the brooklyn theme it doesn't seem like you have an option to change the button color. It changes itself (to black or white) depending on the button color you choose.
Am I completely missing something obvious?
I've tried adding screenshots beneath. Please let me know if you need anything else.