MariaDB 10.3

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CREATE TABLE table_name (
    Id int primary key auto_increment, 
    color varchar(50) 
  );
INSERT INTO table_name (color)
VALUES (''), (''), (''), ('') ;
    UPDATE
    	table_name AS t
    INNER JOIN
    	( 
          SELECT Id, 
                 row_number() OVER (ORDER BY Id) AS rn 
    	  FROM table_name
    	) AS sub
    ON  t.Id = sub.Id
    SET color = (CASE WHEN MOD(rn,3) = 1 THEN '#F00'
    	             WHEN MOD(rn,3) = 2 THEN '#0F0'
    				 ELSE '#00F' END)
select * from table_name ;


Id
color


1
#F00

2
#0F0

3
#00F

4
#F00