Generally, the metrics are marked with green and the dimensions are marked in blue colour.
WHY DOES MY METRIC APPEAR IN BLUE AND NOT IN GREEN?
The coloUr (type) is derived from the selected aggregation rule, not it's datatype.
When this is not set, a column is assumed to be a dimension thus appearing blue.
When picking an aggregation rule, it's shown as a metric and appearing green. While a float value is seldomly used as a dimension, it's still technically possible.