Mix paint using red, yellow and blue give Hex code

Aside from the fact that a hex value is a proportion (each pair of characters represents a decimal quantity), you can't. Paint colors don't mix the way light does. This is why paint stores have libraries of pre-developed colors, plus a set of tints that are more specific, and not digital color wheels.

If you want to approach it mathematically, use a hex converter to get decimal values, then mix that number of parts for each color. Don't expect great results, though, partly since your RGB paints probably aren't exactly FF0000, 00ff00, and 0000ff, and also because compounds tend to change when brought together.

Related: How to convert RGB colors into CMYK (real paint colors)?

Paint stores can custom match any paint color using their equipment. The exact proportion of tints are based on the color sample you bring them and the base color of paint and sheen you select.

Not all paint base colors are exactly white, and they use more than just "red", "yellow", "blue" and "black" to make the color matches. It's been a bit since I last bought paint, but it seems to me the mixer at my local big-box store had upwards of 16 different tint colors to choose from in order to create the desired shade.

I'd suggest that you:

• Sit down at your computer and generate a square of each of the exact hex color combinations you're after.
• Print them on a high-quality ink-jet printer (preferably a photo-quality printer, on photo paper)
  • Alternatively, send it to your local "pharmacy" or other place that'll print photos for you. It might cost as much as $0.25 for each "picture" to do so (in the US, substitute local currency as required).
  • Note that unless you've color calibrated your monitor and printer, your printed sample probably won't be exactly the color shown on your monitor, but, unless you're a professional photographer, it will probably be close enough.
• Bring the picture to your local paint supplier and have them use their equipment to make up a batch of paint to match.

Paint stores will custom mix colors (from either a predefined color chip from among the hundreds they have in stock or a color sample you bring in) for free, you just pay for the container of base paint you're after.

If you've already got paint that you're trying to mix from, I'd submit that you're going to be disappointed in your results, as the "red" you've got is probably not the exact "red" specified by a full FF (or 255) in the red channel as displayed on your monitor. Same goes for your "yellow", "blue" and even your "black". Note, too, that you're trying to mix from RGB as specified in the color picker on your computer and make that from R(YB)B in physical paints. How much yellow and how much green go into making that "blue" hex number you're looking at?

If you've already got the paint in hand, and you're painting a small area that will be fully covered by the amount of paint you've got, and you're willing to experiment, then by all means, approximate the proportions and go for it. (Make sure you use a paint shaker or a paint stirrer "bit" in your drill for a very thorough mixing.) Just don't expect to ever get another batch of paint to exactly match this one without bringing a sample to the store. Some paint will inevitably stick to whatever measuring container you use, so your measured 5ml (for example) won't put exactly 5ml of paint into your mix. You'll probably lose 1ml (give or take) in paint stuck to the measuring cup.