I've been collecting links to various resources. Hopefully, these will be of use to you.
WebAIM's Contract Checker is a nice tool to check if the contrast between the background and the body text is enough for each WCAG level.
WebAIM's Link Contrast Checker lets you compare background, body text colour, and link colour for the cases where you are using only the colour to identify links.
Who Can Use - A great tool that brings more attention and understanding to how colour contrast can affect different people with visual impairments. It lets you compare the background and foreground with text colour and boldness.
Accessible Brand Colors shows you how ADA-compliant your colours are in relation to each other. You can add all your brand colours to this tool and see what combinations of them you can use.
Sara Soueidan's blog post A guide to designing accessible, WCAG-compliant focus indicators. This post also refers to the WCAG 2.2, which is not yet released at the point of writing, so check those examples out and make sure you are already compliant with the new rules as well.