This script is an example of setting the color from code. Is this along this lines of what you're looking for?
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using RaymarchingToolkit;
[RequireComponent(typeof(RaymarchObject))]
[ExecuteInEditMode]
public class ColorInput : MonoBehaviour
{
RaymarchObject obj;
public string InputName;
public Color ColorValue;
void Start()
{
obj = GetComponent<RaymarchObject>();
}
void Update()
{
var input = obj.GetMaterialInput(InputName);
if (input != null) {
input.color = ColorValue;
}
}
}