Change the background color of b-form-checkbox-group

I am struggling to change the default (blue) on checked background color of checkbox rendered through b-form-checkbox-group. Could not find a proper way from the docs of Bootstrap-vue even if it is there.

Code looks like below:

<b-form-group>
  <b-form-checkbox-group
    id="checkboxId"
    v-model="anArrayInDataHook"
    :options="anArrayInDataOrComputedHook"
    name="randomName">
  </b-form-checkbox-group>
</b-form-group>

If it needs CSS modification, then it is fine too. Tried with different approaches but failed. Thanks in advance.