The redundant sequence number only invites errors and wastes space.
This is what a newbie does to fake a sequential file and it is
non-relational.
The look-up table should have the encoding at the primary key and then
a description. After that, you might need temporal data, prior codes
or other things.
Step one is to determine if there is an industry code for the value you
are using in your attribute. In the case of color there are a ton of
them -- Pantone for printing, Land numbers for general industry, and
something Earl Schieb and the automobile industry has for automobile
finishes.
There is no requirement that an encoding be character data; a lot of
them are numeric.
If there is no industry standard, then **carefully design** , not
blindly number, an encoding. Get a copy of SQL PROGRAMMING STYLE for
details on the kinds of encoding, scales and measurements. You might
also want to learn why fields and columns are not anythign alike.