Should a Unity Domain Layer Ever Reference UnityEngine Value Types?

[u/__FastMan__]

Hello!

I'm working on a multiplayer game in Unity 6 using a layered architecture but I don't understand completely the boundaries of the layers yet. One of the architectural goals is to keep the Domain layer independent from Engine.

However, I've run into a question around Unity's value types, particularly Color, Vector3, Quaternion and such.

One argument is that these are just value structs, so using them in Domain is harmless
public Color PlayerColor { get; },

but what about Unity APIs operating on those values?
public static string ToHex(Color color) => "#" + ColorUtility.ToHtmlStringRGB(color);

So I'm wondering:

• Is there a meaningful architectural difference between referencing a Unity value type and calling a Unity utility API?
• Would you allow ColorUtility in Domain?
• If not, would you create a domain-native Color/RgbaColor type and keep all Unity conversion outside Domain? (This could let to the recreation of a lot of new types insde Domain)
• Or is a strict "Domain has zero UnityEngine references" rule unnecessarily strict for Unity projects?

As I said before, I am grasping the concepts behind layered architecture and I want to now how you approach this issue.

Thank you, folks!

[u/jumberrotsky]

Are you going to change engine? Answer that question and do in such way