image -> gradient color.

blink.shader

shader_type canvas_item;

uniform vec4 glow_color : hint_color;
uniform vec4 back_color : hint_color;
void fragment() {
	vec4 text = texture(TEXTURE, UV);
	float flow = sin(-text.g + TIME) * text.a;
	flow = smoothstep(0.5, 1., flow);
	COLOR = mix(vec4(back_color.rgb, 0), back_color, text.a);
	COLOR = mix(COLOR, glow_color, flow);
}