A useful way to do predictable colour grading is to use the Selective Colour adjustment to bend colours towards harmonic sets. This free set of 24 macros does just this, moving colours to sets of three key colours, in each case, based around the colour wheel for the 12 primary, secondary and tertiary colours. Analogous harmonies are based on adjacent colour sets around the colour wheel.
To download the macros, here is the download page, including more detail about how to install and use these.
For related videos, see here: http://changingminds.org/disciplines/photography/affinity_photo/youtube_videos/795_free_macros_analogous_grading.htm#see
There are now online pages for InAffinity here: https://changingminds.org/disciplines/photography/affinity_photo/affinity_photo.htm
Free resources, including macros, palettes, etc. are here:
If you are a beginner, start here:
There is a full, cross-referenced index for every video here: https://changingminds.org/disciplines/photography/affinity_photo/inaffinity_video_index.htm
To find videos by date of publication, start here: https://changingminds.org/disciplines/photography/affinity_photo/ap_time-sorted.htm
To find videos by subject, start here: https://changingminds.org/disciplines/photography/affinity_photo/categories/ap_categories_alphabetic.htm
The web page for this video is here: http://changingminds.org/disciplines/photography/affinity_photo/youtube_videos/795_free_macros_analogous_grading.htm