To welcome attendees with blind or low vision, first speak to your coaches. Someone coaching an attendee with low vision should first and foremost be flexible. An attendee with low vision may already have a screen reader set up on their machine that they are used to, so the installation party is a great opportunity for a coach to get to know this attendee's setup. When hosting a remote workshop, it might be better to have the coach working with any blind or low vision attendees contact them separately so they can discuss how best to support that attendee one-on-one.
Not all attendees who have low vision are blind, so make sure that any presenters giving lightning talks are using a large font on their screen if they are using a presentation in shared view. (Remember that code in particular can be hard to read on a PowerPoint.) Ask your presenters to prepare digital handouts in a large font that can be shared via pdf before the workshop starts (pdf files can be zoomed in on more easily). Ask your presenters to also remember to verbally describe any images that are in their presentations and use alt text for images on digitally shared files.
Make sure the web site and materials you prepare for the workshop pass the Web AIM Contrast Checker. Just feed in the hex code of the background color and the font color, and this free tool will let you know if your contrast is sufficient.
Code in particular can be hard to see for anybody. The font tends to be small and not double-spaced, so if you're doing any demonstrations on a large screen, make sure your font is very large. Finding where to enlarge the type on the command line or in a text editor can also be hard, so have your coaches walk your attendees through that. It will make it easier for them to read and debug.