please any advice?

we have a large decked area around our home made from scaffolding boards this has been so succesful we had another area done i treat the boards every couple of years with cuprinol wood preserver i had half a tin left over and proceeded to stain new decking 3/4 of the way through i ran out and have been unable to match color so i opted for the black ash thought this would go straight over the top !!! all that has happended now is i have alot of miss matched boards and they look alot shinier than the original tin can anyone advice me if i could now undercoat or if i could use something else to cover all many thx carol