This function controls the alpha (transparency) of the sprite on the asset layer. You give the sprite element ID (which you get when you create a sprite element using layer_sprite_create() or when you use the function layer_sprite_get_id()), and then set the alpha value to use. Alpha can be between 0 (fully transparent) and 1 (fully opaque) with the default alpha value for the sprite element being 1. Note that if the layer the sprite element has been assigned to is not visible - or the element itself has been made invisible - you will not see any difference with this function until the layer or element has been made visible again.
Argument Description sprite_element_id The unique ID value of the sprite element to change alpha The alpha for sprite sprite, from 0 to 1 (default is 1)
var lay_id = layer_get_id("Asset_sky");
var spr_id = layer_sprite_get_id(lay_id, "Clouds");
The above code gets the ID value of the sprite asset named "Clouds" assigned to the layer "Asset_sky" and then sets its alpha to a random value between 0 and 1.