How to change these colors?

[reath]

Does somebody know how can I change the following DEFAULT colors:

-Clients placeholder on <q-select>
-Clients helper on <q-field>
-the down arrow in the upper-right <q-select>
-The underline on the <q-select>
-The label attribute on <q-field>

[lucasfernog]

For placeholder, check these CSS selectors: https://www.geeksforgeeks.org/change-an-html5-input-placeholder-color-with-css/

For the other elements, use the browser developer tools to find the element you must target