The colour and tonal information in a digital document is stored as numbers. When we share these documents between devices, the device has to work out how to display the colour. As not all devices can display the same colour gamut it can lead to colours looking different on each device.
To ensure that the colour looks the same on each device, we use colour profiles to tell the device how to display or render the colour information.
In Affinity Designer, an opened file's colour profile is honoured by default. You have the option to convert it to the current working colour space. When placing images into an existing document, the image's embedded colour profile will always be converted to the document's current working space.
On export, you can choose to embed the document's or a named colour profile to ensure accurate colour management. Alternatively, the exported file can be unprofiled by not embedding the document or named profile.
Affinity Designer lets you choose global default colour profiles, assign a colour profile as you create a document, or at any point during your session.
Soft proofing simulates output as you edit and design with respect to the colour profile and the paper medium you intend to print on.
In Affinity Designer, this can be done by applying a Soft Proof adjustment to your project. You can then preview how your output will appear, preventing any nasty surprises at print time.
Because soft proofing is applied as an adjustment you can apply multiple adjustments, and therefore produce soft proofs for multiple output devices.
As an example, if you want to create several different output types, you might want to start with a colour profile on document creation with a wide gamut (e.g., Adobe RGB 1998), and then change the profile to match the output destination. However, colour information may be thrown away if changing to a smaller colour gamut—simply changing back to a profile with a wider gamut will not restore the additional colour information. By applying a soft proof adjustment you prevent this, allowing you to work in a wider gamut until you are ready to change to your chosen output profile.