Word Cloud custom visual: Problem with customising data colors

I've identified the cause of the issue - if my data has any blanks or null items, it seems to cause the data colour option to disappear. When I cleansed my data, some cell contents were cleared. I was able to fix this issue for myself by putting in a placeholder punctuation (which are excluded from my word cloud).

Let me know if you need any further detail. As my report contains confidential data, I would need to mask the data if I were to share it - I'd prefer not to if the above information is sufficient!