CODE EXAMPLE FOR CSHARP

change color unity over time

void Start() 
{
    // ... your other stuff 

    StartCoroutine(ChangeEngineColour());
}

private IEnumerator ChangeEngineColour()
{
    float tick = 0f;
    while (engineBodyRenderer.material.color != endColor)
    {
        tick += Time.deltaTime * speed;
        engineBodyRenderer.material.color = Color.Lerp(startColor, endColor, tick);
        yield return null;
    }
}