It is too dark. A brand color especially if its such a dark one doesn't need to be the entire piece like that.
Look at the histogram of your piece, here's an Answer of mine on Photography explaining a little: Photography.Stackexchange: Can I tell which photo has more contrast from their histograms
In general you want a piece to have a nice full range. And generally speaking more in the lighter areas since our eyes are drawn to light. Kind of the same reason why trade show booths often add additional lighting.
Even though the brand color is a royal blue, it doesn't need to be the entire background. Break the image up to lead the eye from section to section.
Not so much about the color but I'd also say as a whole the banner does nothing to communicate why an attendee should care about the product/service.
Without knowing anything about the product or brand its hard to make recommendations. I would probably look at just adding more to. Maybe some yellow or orange elements to add some brightness and contrast. Gradients could really help a lot as well.
To be kinda brutally honest its flat and minimal in a bad way. It looks like a piece of clipart on a colored background. Nothing was done to lead the eye from section to section or create interest.
Glance over Pinterest: Trade Show Banner. See how there's colors, shapes, text, and especially contrast. Big bold graphics and photos.