How to set chart colours in Numbers for iCloud

Arg. I thought I had it figured out, but inevitably I now can't replicate the problem.

So let me at least describe what I think is going on

• The source data table has dates down the left (count of rows each month) and dates across the top (the day I captured the data, as I'm tracking change over time)
• I Hide the columns I'm not using, leaving only the latest day's worth of data
• So I think this is confusing Numbers; it's trying to guess which is Series & which is Data & concluding that both rows & columns contain Series so it's giving me a multi-series chart - i.e. each bar is a different colour representing a different series of data.

I managed to avoid the issue by Command-clicking the 2 columns I want to plot (column A with the months of the year & column C, for example, with today's stats). But as I say, I now can't replicate the issue...

Attached is a screen print showing the source table & a couple of charts. I had intended to add a 3rd chart showing the problem but, as I say, I frustratingly seem unable to replicate it...

As a last word - I want to express my thanks for everyone who responded to my issue; it's great knowing there's a community out there ready to help, even on a product like Number for iCloud which I imagine is fairly niche