Anyone can access a website (more or less); anywhere, anytime. You never know who will see or interact with what you put online. That's why, if your business is using the internet to reach customers, it is vital that you have it set up to be accessible. Accessibility is unfortunately the most overlooked part of websites, especially ones created with Wix, or Wordpress.
This one might actually be less obvious, even though it affects more people. We want to make sure our content is clear and that it isn't hard to read; have you ever seen red text over a yellow background before? Pretty hard to read.
Anyway... There are 2 elements that control contrast on a website which are: text size, and foreground/background colour ratio. The main bit here is the colour ratio, but lower colour ratios are accetable if you are using them on larger bits of text. If you have some colours you want to check, a great website is WebAIM.
An important thing to note for this is that not only is this to help those with visual impairments (although, that really is the one and only reason one should need) it helps 50%+ of computer users. Eye strain is something that is almost certain for anyone who uses a computer for their job, which, depending on what country you're from, may be the majority of people. Eye strain is made worse by viewing content that has very poor contrast, as well as viewing bright content in a dark room (or dark content in a bright room). So, as well as just general contrast keeping, I'd also recommend a theme picker, so users can alter the website to fit their needs, minimum being light and dark mode.
Just a small aside here really. If you're a global brand, firstly, well done, and secondly, colour is a very important part of the human psyche. Unfortunately, if you want a one-size-fits-all website, you will have to go with neutral colours, anything flashy, such as reds or blues, can evoke emotions and in some cultures, those emotions aren't very good and can make your brand, without even having tried it, make people not want to try it. You can find this in things like low-price items where they use certain colours that might make you think the item is tacky.
There isn't much nuance to this one, just it doesn't get done. With every image you upload, you can also provide it with an "alt" bit of text, which is a description of what the image is, that way blind, or visually impaired users, will get to hear what the image is. This isn't automatic, and screen readers can't do anything without first having the alt; this means you have to manually set it, which often isn't done and sadly in some interfaces is actually a hidden option. Treat this option as mandatory, rather than optional.
I've seen this many times; restaurant menus, holiday itineraries, etc., things that would usually be on a flyer that was just put on a website. Do not do this. If your website does not have the ability to have the content display in the way you want it to, you just need to work on a new strategy, or you need to get the website changed; making the content look the way you want in an image and then uploading it is just hurting your business. The reason for this? SEO. Told you it always comes to this.
Whenever a search engine looks for content on your website, it goes through the text and through the alternative text your have provided. This is why this will be hurting your business. An image is not text so it cannot be read, and unless you write your entire menu, or whatever it is you created in the alternative text meta data, your website in the eyes of Google will be empty. So, if you sell Chicken Korma, and someone Googles Chicken Korma, your product just won't show up, but your competitors who are using a custom-made website menu, they will show up.