Hi @Aizada_M 
You can access and make changes to your color palettes by going to admin-customize-colors. there you will see various color palettes that you change the individual colors that you can change to alter the look of your forum.
The color palettes are used by your forum themes in admin-customiz-themes tab, so I would first have a look in the ones you are using to see which respective palettes they are using so you know which palette to change.
Themes
This is where you can add the various theme components or make new ones, or edit the css and html of various elements. You can see the color palette selector here:
Color Palette
In the colors tab, you can find the respective palettes and the one being used by your theme should be listed in on the left - this is the one you want to edit. Your theme may also have a light / dark palette you can change as well. The Color scheme can be selected by users box will be checked for ones the user can select in their color mode preferences. The palettes include color picker as a well as hexadecimal color fields.
