Thanks, Marlon, for the feedback and your comments.

With respect to SC 1.4.1, the standard is:

"Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element." [Emphasis mine]

Aria attributes aren't relevant for this SC. That's because it's more geared to those with colorblindness. Those with colorblindness (assuming they don't have another disability) typically don't use assistive technology - at least none that would benefit from aria attributes.

My point was that if the only visual difference between an enabled text box and a disabled one is color, that violates SC 1.4.1.

I hope that clarifies things. Thanks again!