Start by clicking ‘Address Book’ -> ‘All Email Lists’
Click On Your Preferred List Where You Want To Change The Subscribe Form Button Color,
Click on Pages Number
Or in Quick Links, Drop Down and Choose “List Pages”
Select Subscribe Form From Sub Drop Down Menu on Right
Go to the Source Code of Your Form
Find the [SUBMIT_BUTTON] Tag
Scroll to the bottom of your source code.
Look Above The Submit Button Tag and Find the ‘btn-primary’ code.
Find and Change the Hex Color Code to Your Desired Color
Click Save changes.
Click The Preview Icon To Preview Your Form With The New Button Color
The Subscribe button color should now be changed.