Calendar Sharing Software?

I’ve been doing a lot of freelance work lately, mainly for one regular client who consistently enlists me for both small and large tasks, I can almost guarantee that I’ll have work to do for them pretty much every day. The problem is that it’s not my full time job, I have a different full time job in which I work 12-13 hour shifts, and my weekends are mostly booked for spending time with my 3 year old son, so my availability to do their work is very limited. I’ll often get phone calls from them while I’m at work, asking if I can quickly do something for them, which is not good. My schedule is consistent, but alternates weekly, which is understandably hard for my client to always remember.

I’m looking for something very simple that I can update regularly, and that my client can see in real time. Really all I need is to highlight days in different colours, and a small label, so they can see exactly when I’m available for phone calls and to do work. Green: Days where I can do work, plus a small label for the exact time I’m available. Red: Days where they shouldn’t expect me to do any work for them. I’ll probably end up doing work here and there on red days, but I’ll have no dedicated time for it.

I’ve tried Google Calendar, but it’s more complex than I need or want for this case. I swear I’ve seen something very similar to what I’m looking for, but I’m not sure where now. If anyone has any ideas, please let me know.

Thank you.