particles/Main.cs

using System.Collections.Generic;
using Godot;

public class Main : Node2D
{
    private readonly List<ParticleType> _particleTypes = new List<ParticleType>();

    public override void _Ready()
    {
        GD.Randomize();
        InitializeParticleTypes(5);
        InitializeParticles(50);
    }

    public override void _Process(float delta)
    {
        if (Input.IsActionJustPressed("quit")) GetTree().Quit();
        if (Input.IsActionJustPressed("reset")) GetTree().ReloadCurrentScene();
    }

    private void InitializeParticleTypes(int nTypes)
    {
        for (var i = 0; i < nTypes; i++)
        {
            var type = new ParticleType
            {
                Hue = (float) GD.RandRange(0, 1)
            };
            _particleTypes.Add(type);
        }
    }

    private void InitializeParticles(int nParticles)
    {
        var typeCount = 0;
        var particleScene = GD.Load<PackedScene>("res://Particle.tscn");
        for (var i = 0; i < nParticles; i++)
        {
            var particle = particleScene.Instance<Particle>();
            GetNode<Node2D>("Particles").AddChild(particle);
            particle.Position = GetRandomParticlePosition();
            particle.Type = _particleTypes[typeCount];
            
            if (typeCount < _particleTypes.Count - 1)
                typeCount++;
            else
                typeCount = 0;
        }
    }

    private Vector2 GetRandomParticlePosition()
    {
        const int padding = 32;
        var viewportRect = GetViewportRect();
        var position = new Vector2((float) GD.RandRange(padding, viewportRect.Size.x - padding),
            (float) GD.RandRange(padding, viewportRect.Size.y - padding));
        return position;
    }
}