20 R1 NOT supporting Label Colors

Use a browser debugger Inspect Element feature to look up the HTML control names and CSS class of the target controls.

For example here I looked up HTML control ‘label’ :

Then modify theme file located in ‘\YourWebsite\\App_Themes\Default\00_Controls.css’ to change the CSS style. 

Here I changed HTML label controls color to red by adding this style:

label {
  color: rgba(255, 0, 0, 1);
}

The About box dialog uses a span HTML control instead of a label.

The control has a CSS class labelH we can target but it also has inline style which will override the CSS style:

<span class="labelH" id="ctl00_usrCaption_pnlAbout_lblAcumatica" style="color:#4E576A;font-size: 22px; font-weight: bold">Acumatica 2020 R2</span>

To have CSS class applied instead of the inline style color you need to add CSS important keyword:

.labelH {
  color: rgba(255, 0, 0, 1) !important;
}

Style properties marked important will be applied even if another style is trying to override it:

ForeColor property works at ASP level but the CSS is applied after that so you need to change CSS.

Examples above target all controls. When you want to target a specific Acumatica editor control you can use custom CSS class. This example is for field SOOrder.Status.

Then lookup the control type with browser debugger, this is an input type control:

To target that element you have to specify your custom style and the name of the control:

.customColor input {
  color: red !important;
}