If you are making a website for your company and you have graphic instructions at your disposal, you should make your site's color and font choices with them in mind. Fonts used in electronic environments are often specified separately in the instructions. The colors can normally be found as Hex color values, which you can enter directly into the theme's settings.
If don’t have any official graphic guidelines, but you have made, for example, printed products (business cards, brochures, etc.), you should try to keep the style of the website the same.
If you don't have any ready-made material from which to draw inspiration for the website, you could choose an image from Unsplash, which color scheme you like, and save it to your computer. There are online tools, such as Adobe's Color, where you can upload an image from your computer and the tool generates alternative color combinations from it (see example below).
When planning the structure of the website, graphic look, and color theme, pay special attention to accessibility. Make sure that all the most important elements and content (for example, contact information) are easy to find and read.
Especially when choosing colors, it's good to keep in mind that, for example, the text should stand out well enough from the background. Colorblind users should also be taken into account when choosing colors.
There are online tools available for testing different color combinations. For example, in Adobe's versatile color tool you can enter two different color values and the tool tells you whether the contrast between them is sufficient.
On the same page, under the "Tools" section, you can also find the "Color Blind Safe" tool, which simulates how people with color blindness see the contrast.