Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

When defining palettes (accent or primary) with CSS variables, the chekmark color of mdc checkboxes is not the right one.

Indeed, on this line, type-of($value) == 'color' is always false when palettes are defined with CSS variables.
When palettes are defined directly with web or hex colors, the mdc checkbox chekmark color is correct.

Reproduction

Steps to reproduce:

1. Create an Angular project with angular 16
2. Run the command ng add @angular/material @angular/cdk.
3. Ad custom theme by defininng palette with CSS variables
4. Add material mdc checkbox to a template

You can reproduce the problem with this demo on Stackblitz.

Expected Behavior

When color 500 of the accent palette is dark, the checkmark of the checkboxes must be white.

Actual Behavior

When color 500 of the accent palette is define by a CSS variable, the checkmark of the checkboxes is always black in a light-theme.

Environment

• Angular: v16.0.0
• CDK/Material: v16.0.1
• Browser(s): all
• Operating System : Ubuntu