Khaki and tan can be worn with black or brown pieces, but not both. Blue, white, maroon and burgundy go really well.
As a rule, pastels won't go with khaki and tan but there are some exceptions such as magenta, orange, and pink when used as part of a pattern.Denim looks good with tan, and khaki as do many tartans including Black Watch.
A denim shirt worn with tan pants looks great as does a Black Watch tartan shirt worn with tan pants.
