How to visualize categorical data over time?
I'll give it a go, but a lot depends on how you want to communicate your results.


try to keep the buckets, and add counts to them, so you end up with something like:



date bucket count
2015-09-11 2-6 6
2015-09-12 2-6 9
2015-09-13 2-6 2
2015-09-11 10-16 9
2015-09-12 10-16 15
2015-09-13 10-16 4



This you can communicate either via a line chart, but I would go with side by side bar charts per period, maybe aggregated to week or month depending your timeline. If you have many ranges, splitting them in different graphs. 


Don't index the ordinal values. The reader of the graph should not look somewhere else to figure out what the numbers mean. Just use counts with the ordinals and use line charts or bar charts, summary tables or a cross(table)
Count the occurences and use side-by-side or stacked bar charts and color the bars according to the colors you have. But human perception will always give a higher bar / line / area more weight than a smaller / lower one. Or just represent it as a table. That way you don't give any opinion except that some colors might occur more frequently than other.