We are slowly moving towards a platform-wide, consistent color palette but right now even the new UI in the Beta Preview isn’t the fully final palette. Partially because our design teams are still coordinating and partially because the new colors don’t work well with old UI.
But once we get further along, there will be standardized color tokens you will be able to use. We will recommend against using color values directly because that’s what got us into this color mess to begin with 
In other words, we won’t ever get to allowing theming or color customization if people keep hardcoding colors.