particles/ParticleSimulation/ParticleType.cs

using System.Collections.Generic;
using Godot;

public struct ParticleRelationshipProps
{
    public ParticleRelationshipProps(float minRadius, float maxRadius, float force)
    {
        MinRadius = minRadius;
        MaxRadius = maxRadius;
        Force = force;
    }

    public float MinRadius { get; }
    public float MaxRadius { get; }
    public float Force { get; }
}

public class ParticleType
{
    private readonly Dictionary<ParticleType, ParticleRelationshipProps> _particleRelationships =
        new Dictionary<ParticleType, ParticleRelationshipProps>();

    private float _hue;

    public float Hue
    {
        get => _hue;
        set => _hue = Mathf.Clamp(value, 0, 1);
    }

    public void AddRelationship(ParticleType type, ParticleRelationshipProps props)
    {
        if (_particleRelationships.ContainsKey(type))
            return;
        _particleRelationships[type] = props;
    }

    public void RemoveRelationship(ParticleType type)
    {
        if (_particleRelationships.ContainsKey(type))
            _particleRelationships.Remove(type);
    }

    public ParticleRelationshipProps GetRelationship(ParticleType type)
    {
        return _particleRelationships[type];
    }
}