Visually categorizing table columns?

In our data table, we have three types of columns. Let's call these Type A, B and C. There is only 1 column which is Type A, maybe 4-7 columns that are Type B and the rest are Type C (the least important).

Does anyone have suggestions for how to visually communicate these categories of columns? I thought about using an icon of sorts, but it seems a little bulk because our table is so crowded. Thanks.