Affinity Designer can use different color models to represent different ways of describing color. These models (RGB, CMYK, Lab, and Gray) can be selected as you create your new document.
Color definitions are described comprehensively on the internet, so in this section we'll just focus on how to set a color model, the model's color space, and how a color profile represents that color space.
In terms of selecting color as you design, Affinity Designer provides the Color panel's HSL color wheel by default or optional sets of sliders. Furthermore, the Swatches panel can be used for easy access to preset and custom 'saved' colors that you'd like to use again.
If you're happy to leave color management until output is required, you can create new documents with the suggested default color format RGB/8 with sRGB IEC61966-2.1 color profile.