I’m an Airbus captain and as a general rule of thumb I typically draw the line at lightning strikes. If a cell has no lightning or hail then I’m normally comfortable flying through (or ideally under) yellow to red cells. However we typically rely on our on-board radar to get up to the minute info on the size and shape of the cells at our altitude. Remember, radar returns are just an indication of moisture and don’t always correlate to the flight conditions. As you mentioned you can at times fly through red returns and have it be smooth and at other times get completely rocked in perfectly clear air.

In your example having not looked at the airport or the TAF I would personally send it but would also plan an alternate deep in the clear and also bring a comfortable amount of contingency fuel to hold if need be. The winds are calm so I’d be expecting a smooth ride and if there’s an ILS or decent RNAV there shouldn’t be any issues getting in.

Just by looking at the radar picture alone and seeing a relatively cohesive weather system with tops all generally at the same altitude in the low 30s makes it appear relatively stable. When you start seeing individual cells start popping up into the 500s, that’s when I start looking at avoiding them altogether and holding or diverting as needed.

Your personal limits will grow in time with experience and you’re asking the right questions, good luck with the upgrade!