Q: tikz: removing borders in fill white This is what I got with the following  code

\documentclass{standalone}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}

\fill[blue!20] (90:4) -- (210:4) -- (-30:4);
\fill[white] (90:4) -- (190:2.6) -- (-10:2.6) ;

\end{tikzpicture}

\end{document}

I wonder how to remove borders in fill. Thanks
Edited
Using the solution given by @Ulrike Fischer, I get something like this

\documentclass{standalone}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}

\fill[blue!20] (90:4) -- (210:4) -- (-30:4) -- cycle;
\fill[white, draw = white, thick] (90:4) -- (190:2.6) -- (-10:2.6) --cycle; 

\fill[green!20] (90:4) -- (190:2.6) -- (-10:2.6) -- cycle ;
\fill[white, draw = white, thick] (90:4) -- (155:2) -- (25:2) -- cycle;


\end{tikzpicture}

\end{document} 

This appends extra space between two pieces.

A: You can try to draw the smaller triangle explicitly:
\documentclass{standalone}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}

\fill[blue!20] (90:4) -- (210:4) -- (-30:4) -- cycle;
\fill[white,draw=white,thick] (90:4) -- (190:2.6) -- (-10:2.6) --cycle ;

\end{tikzpicture}

\end{document}



A: In your original code, you don't have borders. The the border effect is generated because the blue triangle is drawn first then the white triangle (which has smaller dimensions) is drawn on top of it, hence a border is generated. You can achieve your desired output by slightly changing your coordinates:
\documentclass{standalone}
\usepackage{tikz}

\begin{document}
  \begin{tikzpicture}
    \fill[blue!20] (90:4) -- (210:4) -- (-30:4);
    \fill[white] (90:4.5) -- (190:2.615) -- (-10:2.615) ;
  \end{tikzpicture}
\end{document}


Now for @Ulrike Fischer answer, though it is good and unique, the same problem occurs. The solution requires to draw 4 distinct shapes (one is overdrawn by two triangles which is giving resulting in that border effect). Try to comment \fill[white, draw = white, thick] (90:4) -- (190:2.6) -- (-10:2.6) --cycle; and change your colors to solid blue, red and black (for better visualization) and you will see a better result, but the problem persists at a lower significance.
