You can set custom colors in several ways.
Color Mixer - Scroll left or right along the color mixer (the palette on canvas by the tool wheel) to access your color palettes of custom colors. You can set these palettes in the Colors menu via a tap+hold on the color circle in the center of the tool wheel. Tap a color to apply it to your tool. You can also tap+hold the color mixer to blend the colors in the palette together, and find colors complementary to your project. Slide your finger along the blended colors and let go to choose that color (as displayed in the color circle in the wheel).
Color Palettes - If you tap+hold the color circle at the center of the tool wheel, you’ll access the Colors menu. Here you’ll see palettes you can customize via the COPIC color wheel (tap on the Current Color circle to open it), by entering your color’s COPIC, HEX, RGB or HSB value into the appropriate field, via the full-spectrum sliders beneath these fields, or by dragging and dropping them into a palette from another app. Tap+hold+drag a color from the color circle or wheel or other app to pull it into a palette. You can choose up to eight colors in each palette.
Tap a palette to set it to your on-canvas color mixer. The palettes will appear in the order you tapped them in. Read here for an in-depth walkthrough on color palettes and color mixing.
Color Picker - Our color picker allows you to choose colors or tools from any stroke drawn on the canvas, or pick colors from any image or screenshot imported onto the canvas. Choose a color to set it to your current brush. Use the Most Recent dynamic palette to drag these custom colors into a long-term palette in the Colors menu. Read more on the color picker here.
Imports - Some supported apps allow you to drag+drop a color from one app into another (like Concepts). As described with the Color Picker, you can also import images and screenshots of specific color palettes onto the canvas (such as a full spectrum wheel) to make color picking simple.