ChatGPT doesn't seem to be too helpful, but I tried a little more. Here's how it went:

Me: "Sorry. I'm using gotot 3. Label doesn't seem to have .modulate."

Apologies for the confusion. In Godot 3, you can achieve the gradual color change effect by using shaders. Specifically, you can create a shader material for your Label node and manipulate the color in the shader code.

Here's an example of how you could achieve this:

1. Create a new shader material for your Label node.
2. Attach the shader material to the Label node.

In the shader code (GDScript Shader Language), you can create a simple fragment shader that modifies the color over time. Here's an example shader code:

shader_type canvas_item;

uniform vec4 base_color : hint_color = vec4(1.0, 1.0, 1.0, 1.0);
uniform float color_change_speed : hint_range(0.1, 5.0) = 1.0;

void fragment() {
    // Calculate the time-based color change
    float time = mod(TIME, 1.0);
    vec4 modified_color = vec4(1.0, time, time, 1.0);

    // Apply the base color and the modified color
    COLOR = base_color * modified_color;
}

In this shader code:

base_color is the initial color of your text. color_change_speed controls the speed of the color change. You can modify this shader code based on your specific requirements.

Remember to set the shader_material property of your Label node to the shader material you created. You can then control the color change speed by adjusting the color_change_speed uniform in your script.

Me: "What about set_color after giving the control node a theme? Would that be a good way to do this? I haven't been able to get set_color to work, as I can't figure out what name and theme_type should be."

In Godot, the set_color function is often used to set the color of certain elements, but it requires a valid name and theme_type from the current theme. Unfortunately, working with themes in Godot can be a bit tricky, and it might not be the most straightforward way to achieve a gradual color change effect.

If you are set on using themes, you could define a custom theme and update it programmatically. However, for your specific case of a gradual color change, using shaders or directly manipulating the color property in your script would likely be more straightforward.

Here's an example using the modulate property of a ColorRect containing the Label:

extends Control

var label: Label
var color_rect: ColorRect
var color_change_speed: float = 1.0

func _ready():
    label = $Label  # Assuming your Label node is named "Label"
    color_rect = $ColorRect  # Assuming your ColorRect node is named "ColorRect"
    
    # Call a function to start the gradual color change
    start_color_change()

func start_color_change():
    # Schedule a function to be called every frame
    set_process(true)

func _process(delta):
    # Gradually decrease the red component of the color
    color_rect.modulate.r -= color_change_speed * delta
    # Set the modified color to the label
    label.modulate = color_rect.modulate

    # Check if the red component has reached a certain threshold (e.g., 0)
    if color_rect.modulate.r <= 0:
        # Stop the color change

The above code got cut off. Here's the continuation and completion of the code:

        set_process(false)

In this example, the color change is applied to the modulate property of the ColorRect, which in turn affects the modulate property of the Label. Adjust the speed and conditions based on your specific requirements.

Remember to replace "ColorRect" with the actual name of your ColorRect node.