ColorMime is a simple plugin for Sketch which allows you to quickly duplicate any Colourlovers palatte in your sketch project. Simply create a rectangle of any size, run the plugin and paste the palatte URL into the prompt window. ColorMime will automatically build the palatte using the original rectangle as a sizing template.
Color Contrast Analyser for Sketch
A Sketch plugin that calculates the color contrast of two selected layers and evaluates it against the WCAG. The test may pass AAA, AA or fail because of a lack of contrast. And even when you do not need to meet those requirements, you can get a feeling for the contrast when you get used to the values. This might help you design accessible content.