Which colors should i use?

Dark blue background, bright yellow print.

I believe red attracts the most, and white is the best font color for a red background.

Purple and gold.

There was a reason that highway departments use blue or green background and white lettering.

https://en.wikipedia.org/wiki/Vienna_Convention_on_Road_Signs_and_Signals

Red is a highly popular color in marketing because it’s bold, captures attention and can evoke powerful psychological responses. Red represents power, energy, excitement, passion and urgency. The urgency response is often a reason why fast-food chains and clearance sales frequently feature red. To separate your ads from other brands that use red, experiment with different shades, as even minor changes in saturation might cause customers to associate that specific shade of red with your brand.

Green can evoke feelings of harmony, health, loyalty and safety, making people feel welcome and secure. Stores frequently use green to help customers feel more relaxed, which can encourage them to be more decisive. It also reminds people of nature, so it’s a popular color with eco-friendly brands. Some people also associate green with money, which can lead to consumers associating a brand with a sense of wealth.

Blue is a trustworthy color that can put people at ease, reminding them of reliability, confidence and security. Brands that aim to build a sense of trust with their customers, such as finance and health care organizations, commonly use this color. Many social media platforms also use blue because some people associate it with intelligence and communication. Blue can also stimulate productivity and indirectly boost sales by soothing anxiety.

What are you advertising on the billboard? Is it a product or a service? Or are you looking for general ideas for what make billboards more attractive?

Colors are a piece of it, design is another. I remember seeing “3-d” billboards with like Chick-Fil-A board with the cows physically off the board, looking like they were painting it. I’ve seen other billboards like this catch the eye and make drivers look.

When it comes to billboards, less is more. The most effective billboard ads tell the story visually instead of with language. It’s less about color psychology and more about readability. That means clean fonts and good contrast. Use this color contrast tool to confirm that there’s sufficient contrast between the text and the background.

As for colors, I would work on matching the aesthetic of your branding and images/graphics. Reds and oranges do draw the eye, but a human face is extremely magnetic to our eyeballs, we’ve been programmed for millions of years to recognize them and read the expressions.

I’m not sure what you mean by “engineering themed.” Are you recruiting students to an engineering program? are you representing an engineering firm and want to instill confidence in the work they do for a local project? or is it something totally unrelated and you’re using engineers to sell it, like mini engineers assembling gummy bears with cranes?