Some guys will use a Acrylic Uerthane Base coat & just not clear it (Not recommended), or spray a flattened Clear over it .
But most are using a tintable sealer to get the color they want.
Todays paint is getting so high priced that if you use a tinted sealer it doesnt take as much TOP color to get coverage.

I highly dont Recommend using just a sealer, UNLESS you use a Clear with flattening agent over it as sealer has NO UV protection ,
plus sealers will in time break down & let moisture through to the steel ! Then if you ever decide to put SHINY paint over it , you just might start seeing little bubbles in the paint , that is caused
by rust popping the paint off from the buttom.

SprayTech