same color (black) used for a 0 (zero) and for missing value?

[mfeather0]

Apologies in advance, I am only just beginning to use Tracy.
It SEEMS that if a column has numerical values, but some of the rows do not provide a value, both a value of 0 (zero) and a missing value get colored the same, namely black.
If so, is there a way to make these different? (my workaround has been to put in a string value to distinguish from 0)