for Template Toolkit this macro will do it This does it using CSS classes for coloring but setting it in a different way works as well.

create a block macro
[% MACRO alt_color(loop_count) BLOCK %]
  [% IF loop_count % 2 == 0 %]
    color1
  [% ELSE %]
    color2
  [% END %]
[% END %]

in your template you do
loop.count is a special property of the iterator
[% FOREACH thing = things %]
  <td class=[% alt_color(loop.count) %]>[% thing %]</td>
[% END %]
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for H::T you can do

<tmpl_loop name='things'>
  <td class=<TMPL_IF __ODD__>color<TMPL_ELSE>color2</TMPL_IF>> thing</
+td>
</tmpl_loop>

you need to make sure you have loop_context_vars set to 1 in H::T to h
+ave access to __ODD__/__EVEN__
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