The header is for a linkedin personal profile. The size is 1584 x 396.
sans-serif like gotham, montserrat, raleway, roboto etc.
You are not limited to just these colors because it's most important that the design goes well with linkedin colors (blue/gray). Feel free to experiment.
I have a feeling that a lighter bluish/purple gray color #dfe3ec or #d4e4ef tweaked to match linkedin would be a good starting point for the background but please try your own designs.
The header design does not have to be blue but it should not have a strong contrast that makes it distracting if it is another color. The header should fit in well with the surrounding page.
The header should be clean and not too distracting with text easy to read.
The design needs to handle the fact that a user profile picture will overlay the design in the bottom left corner so it would be best that the logo and headlines are aligned to the right.
The left side could have some visual background element to make the header more interesting, maybe something to do with blockchain technology. The entire header could have some kind of background but the text must be easy to read.