thisform.Grid1.Columns(5).DynamicbackColor=thisform.IsWhatDayr() is correct. Show us the code for IsWhatDayr(). That is where the problem lies.

Consulting help:
Column.DynamicBackColor [= "cExpression"]
cExpression specifies a character expression [that] evaluates at run time to a single color value.

For a simple example say you want the column to change color depending on the sign of a number:
thisform.Grid1.Columns(5).DynamicbackColor="iif(number >= 0, rgb(...), rgb(...))"

You can generate the value any way you want (literal, expression, function, magic, ...). The result must be a character string that can be evaluated at run time.

I take issue with CarlWarner's code.

1 - A form method must be preceded with a form reference (e.g. thisform.RecordColor())

2 - As written RecordColor() is evaluaated once, and returns a number. This is wrong for 2 reasons:
  a - DynamicbackColor requires a string.
  b - The string must be an expression that can be evaluated every time the grid is refreshed.


For what it's worth in regard to future questions:
"I would still like to see some code to set the backcolor with a procedure." was too vague, ambiguous, ???
"thisform.Grid1.Columns(5).DynamicbackColor=some_procedure()" was perfect!

Please think thru questions as though you were one of us. Help us "get it" the first time.