Utilities

<..fix colortbl..>+
 \def\begin:current@color{\let\sv:curcolor=\current@color}
 \def\end:current@color{%
    \ifx \current@color\sv:curcolor
    \else \csname a:text-colortbl\endcsname \fi
 }
 \NewConfigure{text-colortbl}{1}
 \def\GET@column@color{}
 \def\color:ii[#1]#2#3<.par del.>{\def\:temp{#1 #2}}
 \def\color:i#1#2<.par del.>{\def\:temp{#1}}
 -_-_-

We introduce css for color of text in a cell, only if the color changed in the cell. The last color is the that takes effect.  
 \Configure{multicolumn}
    {}{}
    {\ifvmode\IgnorePar\fi
     \HCode{<div class="multicolumn"}\HColAlign\HCode{>}%
     \expandafter\MUL:LMN\meaning\@preamble//}
    {\ifvmode\IgnorePar\fi \EndP\HCode{</div>}} -_-_-

<..fix colortbl..>+
 \let\ctbl:mcol=\multicolumn
 \def\multicolumn#1#2#3{%
    \ctbl:mcol{#1}{#2}{#3}%
    \expand:after{\expandafter\MUL:LMN\meaning\@preamble}\MUL:PA//%
    \ignorespaces}
 {
   \def\MUL:PA{\gdef\MUL:PA}
   \def\MUL:LMN{%
   \catcode‘\C=12
   \catcode‘\T=12
   \catcode‘\@=12
   \catcode‘\c=12
   \catcode‘\o=12
   \catcode‘\l=12
   \catcode‘\r=12
   \catcode‘\t=12
   \catcode‘\e=12
   \catcode‘\m=12
   \catcode‘\p=12
   \catcode‘\d=12
   \catcode‘\i=12
   \catcode‘\b=12
   \gdef\MUL:LMN}
   \MUL:LMN#1CT@color #2@tempdimb#3//{\::KOLOR{#2}}
   \MUL:PA{CT@color @tempdimb}
 }
 \def\::KOLOR#1{\if :#1:\else <.set to preamble color.>\fi}
 \def\:KOLOR{\@ifnextchar[\mc:clr{\mc:clr[]}}
 {
   \catcode‘\{=12
   \catcode‘\}=12
   \catcode‘\(=1
   \catcode‘\)=2
   \gdef\mc:clr[#1]{#2}((%
        \def\current@color(\if :#1:\else #1 \fi #2)%
        \csname a:cell-colortbl\endcsname
      )\def\:temp##1//()\:temp)
 )
 \NewConfigure{cell-colortbl}{1}
 -_-_-

<..set to preamble color..>
 \:KOLOR#1//%
 -_-_-