I've had them look both better and also not as good. I've been growing Arabian Night for about 5 years. Some years it's blah, and then there's this year, where everyone comments on how gorgeous it is. I ordered 10 from Swan Island this year, and so far 4 have bloomed. One is too early to tell if it's as good or not, 2 are much more richly colored than the online catalog, and on the 4th, it's about the same, but maybe a little paler.
I've noticed that the weather and placement (how much sun and what is growing around them) have a huge difference

Most of the dahlias I have ordered from Swan Island do look like the pictures in the catalog. I also have noticed that depending the weather the colors are different. Mine are much more vibrant once fall comes around and the temps are cooler. I think the hot summer weather fades some of them.

Linda

This is common issue with people who are new to dahlias. First, may I comment that dahlia pictures are taken to flatter the flower and to encourage you to buy it. Seed sellers have been doing this for over a hundred years when they put color pictures of flowers and vegetables on the face of the seed packet. Growing dahlias is like growing any other flower and it does take some gardening skills. The first challenge is to get them to sprout out of the ground, 90% of the time when someone says their dahlia did not grow, it was eaten by a slug or a snail. You need to control them.

As far as the colors of the flowers, do as the other person said and look up other pictures of the flower on a google search and then make up your mind. Remember that some dahlia varieties do fade in bright sun while most do not. And also, most dahlia sellers will replace varieties if they do not grow. Send an e mail and a list to whomever you bought them from and they will probably make it right next year.
Growing dahlias can be quite rewarding and if possible look up a local dahlia club for help and possibly some free or very inexpensive tubers along with their advice.

I guess there are a lot of factors that affects the growth of dahlia flowers like the soil, the variety and, of course, the weather. With good sunshine and enough water, your dahlias should turn out just fine. Don't forget to post some pics if you manage to pull off awesome flowers.

Swan puts a disclaimer in their catalogue about their pics sometimes not matching due to pre-press ink colors etc.

But I have had every experience dealing with names and colors that everyone here posted and I am convinced some dahlias are just hard headed. I had (the equivalent of) Awe Shucks (from Connells?) bloom last year and it was so YELLOW after the first bloom that I moved it from the orange section to the yellow section this year. So what does it do? It's been every bit the orange I thought it was supposed to be originally. I only moved it 8 feet away - same soil, ground, feeding and watering.

I planted a store bought smallish rust orange tuber, planted it in the orange section in the ground and it barely bloomed at all last year. Got perhaps 6-7 small flowers. Color was 'muddy' - not at all what I thought it was supposed to be. So I moved it to a container in the 'graveyard' and this year it has been spectacular. Numerous blooms off a taller plant with rust orange blooms starting out reddish orange.

The bottom line (IMHO)is that like others have said, so many factors can affect size, color and hardiness that I suspect few identical dahlias look and grow the same in any 2 gardens. I've learned to be patient (up to 3 years of no blooms even) as long as the plant looks healthy and simply accept what you get. For a color coordinated gardener like me, this advice drives me nuts but it is reality in a dahlia world. Dahlias just aren't like roses which always look like the box!

DCR

Definitely, the colors are never quite what is advertised. A few times they've turn out to be a daisy-looking style rather than a rounder shaped flower.