In order to obtain aluminum gutters with a pre-finished color which "matches", or comes close to your color, you may need to contact an actual Gutter Contractor. Most Gutter supply houses specialize in selling the various components as well as gutter coils which the contractors then use on their machines to make the gutter. Some Gutter Supply Houses MAY offer to run off, and sell you sections made to order.
But in my area, they've stopped doing that because it's just not worth the hassle. After all, their real business is in selling parts and coil stock to the contractors who've purchased the seamless gutter machines for $7,000-10,000 each.
You might find one of these Gutter Contractors willing to show up, and simply run off the sections you need right at your house.
I used to do that myself as I don't own a machine, but anymore the difference between what they charge to do-it-all, and just run off the sections, is not great enough to make it worth my time.
Lastly, as a previous poster mentioned, seamless is the way to go.
And, all pre-finished gutter I've ever worked with can be painted right over without the use of primer. Just make sure it's clean and dry.
One OTHER last thing, most of the gutter and downspouts I've ever seen, avaialable at the big box stores, are of a thinner gage, and only available in 10ft. lengths.
One who enjoys helping with roof problems, for the fun of it.