Unless I understood something wrong. there seems to be a bug in the documentation. Check help colorspec
... {textcolor | tc} {<colorspec> | {linetype | lt} <n>}
The following code should give a xlabel with a textcolor of linetype 1
set xlabel "myLabel" tc linetype 1
plot x
However, you will get an error message:
colorspec option not recognized
Whereas lt 1 works ok.
set xlabel "myLabel" tc l 1
plot x
Sorry, I don't see how I can delete this ticket, since it was submitted twice...