Fix Color8 constructor using wrong value range

Fix #5015

modules/gdscript/gd_functions.cpp

@@ -1010,11 +1010,11 @@ void GDFunctions::call(Function p_func,const Variant **p_args,int p_arg_count,Va
 			VALIDATE_ARG_NUM(1);
 			VALIDATE_ARG_NUM(2);
 
-			Color color(*p_args[0],*p_args[1],*p_args[2]);
+			Color color((float)*p_args[0]/255.0f,(float)*p_args[1]/255.0f,(float)*p_args[2]/255.0f);
 
 			if (p_arg_count==4) {
 				VALIDATE_ARG_NUM(3);
-				color.a=*p_args[3];
+				color.a=(float)*p_args[3]/255.0f;
 			}
 
 			r_ret=color;