It looks like it could be a sanvitalia. You really could get a better response to your question if you can describe what sun exposure the bed has, how tall you wish the plants to get and any other pertinent details.

Hi calliope
The bed is in full sun. I want to find plants that are less than 12-15 inches tall. I was thinking about blue wave petunia but cannot find anything bright yellow. I don't want to put yellow petunia because it's not yellow enough.

How about Marigolds for yellow?

They are "Golden Sovereign" for a reference, their current height is 11"-14":

{{gwi:3675}}

Gazania "Kiss", current height is 4":

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I was going to suggest Marigolds for yellow, too. Also, some shorter varieties of Zinnia.

For blue, while I love petunias, keep in mind they have a tendency to peter out unless cut back about mid-season. I've never grown the "Wave" series so not if that's the story with that series, too. Not a big issue if you have a handful of petunias to cut back, but if you've got a large bed = work, and can look cr*ppy until they fill in again.

Ageratum would be a great choice for blue, there are short and mid-height varieties. Leilani Blue (? sp) is a lovely mid-height one, ~12", give or take. Ageratums are usually mid-blue, though, not deep blue.

For rich, deep blue/purple, Heliotrope "Marine" is a beautiful choice!

Definitely a sanvitalia on the photo. I would vote for Zinnia Zahara Yellow (really disease resistant) I'm partial to Salvia farinacea for a blue - there are plenty of dwarf varieties available

izhar: That color of marigold is beautiful. I had orange ones last year. I don't know why I didn't think of them. Gazania is definitely not yellow enough for me.

mxk3: I love the profusion of petunia. And yes, they peter out. My husband call them monster spiders :). I was thinking to have petunia in the middle and a border of any bright intense yellow flower. I'll check those you'd suggested out. This is the bed I am planning:
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globlugal: I had Salvia last year, not so crazy about them. Now I have to find a source that sells sanvitalia seeds.

tlan,

I second goblugal's vote for Zinnia Zahara Yellow. The Zaharas, like the Profusions and Pinwheels, are resistant to powdery mildew.

Incidentally, the best Sanvitalias are available as plants. Proven Winners has several choice cultivars of Sanvitalia.

ZM
(not associated with any product or vendor mentioned)

tlan, for a reference that Gazania is from "Kiss Lemon Shades" from Goldsmith seeds.... "Golden Yellow", "Frosty Yellow" & "Yellow" would be better options.. keeping in mind the height you want..

The thing to keep in mind with gazania is that the flowers only open with it is sunny. What wasn't you didn't like about Salvia farinacea?

I grew bi-colored marigolds with blue lobelia in 2009, i didn't get enough marigolds but the color combination was pretty. The lobelia was hit or miss for me, sometimes it was blooming, a lot of the time it was not. If you'll excuse the fact that the bed needs weeded and the lawn is disgraceful...
{{gwi:3678}}From Garden shots 2009

Also, I bought a yellow petunia seed from Park's this year, I haven't started winter sowing my annuals yet but here's a link to what I bought

Here is a link that might be useful: Petunia Dolissima Limoncello

Annual lobelia, especially the darker blue varieties, would work in your cooler zone four summer. It get hot enough here in zone7 that they peter out in mid July. But I saw some in Scotland a couple of years ago in August that were so incredibly full and florific.

I love true blue and yellow beds, especially spiced with a bit of white.

Kimka

A few suggestions that i have grown..........
blue=scaevola,salvia,petunias,forget me nots,ageratums,allysum.
yellow=zinnias,marigolds,lantana,coleus,small bedding dahlias,melampodium,portulaca(moss rose),purslane.