Hi Vik,
I don't know why it didn't work, I have tried what you did above. I tried exact the same thing with categorical variables and table. There should be reason why it does not work, otherwise it looks like a bug.
I have done this kind of thing before with cell arrays as follows. You can try it, it works.
f = uifigure;
cnames = 'Blue'; % Column Color Data
cVars = {{'Blue','Red'},[]}; % Column variables for Colors column and empty for second column. (If you don't want to make the other columns dropdown you should put [] for each column)
w = [400]; % Second column data
tdata = {cnames,w}; % Your table data (You should define it as cell array, if you define as a table 'ColumnFormat' property becomes useless)
uit = uitable(f,'Data',tdata,'ColumnEditable',true,'ColumnFormat',cVars,'ColumnName',{'Color','Wavelength'}); % table creation with ColumnName (this will be your table data's variables right now)
%% Now change cVars as 3 categories as new cVars
cVars_new = {{'Blue','Red','Green'},[]};
uit.ColumnFormat = cVars_new; % Change uitable's ColumnFormat property with the new variables.
