This is part of the new Theming overhaul implemented as part of 8.0.13.
If you look into
Inductive Automation\Ignition\data\modules\com.inductiveautomation.perspective\themes\light\commoinput-field.css, you’ll see the following:
border: 1px solid var(--border--disabled);
This is what is styling your input fields when they are disabled (
--input-disabled is a named color in the variables.css file within that same
themes directory). If these values are not to your liking, you can either bind your own in-line Style properties for the component to the disabled state, or you can customize your own custom theme to override the default values. I recommend reading up on this post. For an idea of what you should probably do, I’d recommend looking at a followup in that thread.