The database screenshot
Perhaps the Chemical Name was pasted from the clipboard into the Chemical name field?
There are two ways to format the data you see in a field. You can specify a format, such as your blue text color, by selecting the field object while in layout mode and specifying a color. But you can also paste text that is already formatted into a field or select text in a field and use the formatting tool bar to format it. This formats the data in the field and this format supersedes any format specified for the field object on your layout.
If this is the cause of your trouble, changing your expression to:
TextFormatRemove ( BrandName & " / " & ChemicalName )
will result in uniformly blue text.
To keep text from retaining any formatting when pasted into a field, give that field the following auto-enter calculation:
TextFormatRemove ( Self )
and then clear the "do not replace existing value..." check box.
You have once again nailed the problem and provided the solution. Almost all of the chemical names were cut and pasted from manufacturer web sites.