I am developing a star chart. As of now, I am using pure black color (HTML #000000) for the background to display the stars on. I have a sample that was printed by Posterbrain, and that was laminated. It has come out well, but the black color is very shiny (i.e reflective). There is also a light blue color on the chart as background for text, which is nowhere near as shiny. From this, I am thinking that the shinyness is due to the black color, as opposed to the laminate. So is there a better dark color I can use which would not be so shiny when it is printed? If so, how do I figure out the HTML color of such a color?
Ink is shiny. The more ink you have the shinier it gets. A solid black [which may actually also have a fair amount of blue underneath it to enhance the 'blackness'] is going to be pretty well saturated in ink.
Some inkjet printers can use either this normal 'photo black' or an alternative matt black, but how well this works can be paper-dependent.
The pale blue, is of course, less shiny because it uses far less ink.
You need to talk to your print service about substrates, inks & laminates.
You can also get matt laminates.
It could be that they are equally glossy, but the highlights just have a bigger contrast against the black background.
Impossible to tell without close-up photographs or, better, physical samples.
Your safest bet, is to use a printer service that offers a mat coated paper.
If you're feeling adventurous, then here's a hypothesis:
Fact: HTML colours use the RGB color space, your printer needs (most likely) CMYK color combinations to reproduce these colours on print. Your printer controls this RGB to CMYK conversion.
Hypothesis: Your poster was digitally printed using a xerographic process. The light-blue was produced with halftoned combinations of C,M,Y and K. The half-tone patterns roughened the surface, effectively softening the gloss, whereas the color conversion of your printer was configured to produce the HTML black using a solid layer of K toner preserving the smooth surface of the gloss coated (not laminated) paper.
If hypothesis is correct, then the slightest deviation from pure black (eg. a very, very dark blue) will result in a composite color with halftones, roughening the printed surface and reducing the gloss of your night sky.
But again... a mat paper is the easy solution.
Depending on the printer/vendor you use, to get the gloss vs matte separation you're looking for is to print all on a gloss paper stock and then spot matte UV the black background. Or the reverse - print overall on matte stock and spot gloss UV the stars. Posterbrain doesn't offer this option - other vendors do. Check with them but offer them the image first and ask what's possible. Without seeing the artwork, we can only answer generally.