Tk4 has a Motif compliant look and feel (LAF).  If you want a more
conformant Motif LAF, put:

set tk_strictMotif 1

as close to the beginning of your program as possible.  Tk reads that
variable dynamically to determine whether it should maintain a strict
Motif LAF.

Tk4 strives to be Motif compliant and does not currently use either
XView or Xt based widgets in its user interface, so an OpenLook
compliant (or similar toolkit) interface is not possible.

Tk8 has native LAF for Windows and Mac (with Unix maintaining the Motif
LAF).  Tk8 uses the LAF of the system it is on without exception.  You
can get the Tk4 LAF on non-Unix platforms only by modifying the core
files to use the Unix widget counterpart code.