[Tex/LaTex] Drawing concentric circles with alternating colors by means of \foreach in TikZ

foreachloopstikz-pgf

I would like to draw concentric circles like these:

enter image description here

by means of TikZ and \foreach command. The way I achieved it is very elementary (and burdensome):

   \documentclass[standalone]
   \usepackage{tikz}
   \begin{document}
   \begin{tikzpicture}[scale=0.2]
   \coordinate (O) at (0,0);
   \fill[red!70] (O) circle (20);
   \fill[white] (O) circle (19);
   \fill[yellow!70] (O) circle (18);
   \fill[white] (O) circle (17);
   \fill[red!70] (O) circle (16);
   \fill[white] (O) circle (15);
   \fill[yellow!70] (O) circle (14);
   \fill[white] (O) circle (13);
   \fill[red!70] (O) circle (12);
   \fill[white] (O) circle (11);
   \fill[yellow!70] (O) circle (10);
   \fill[white] (O) circle (9);
   \fill[red!70] (O) circle (8);
   \fill[white] (O) circle (7);
   \fill[yellow!70] (O) circle (6);
   \fill[white] (O) circle (5); 
   \fill[red!70] (O) circle (4);
   \fill[white] (O) circle (3);
   \fill[yellow!70] (O) circle (2);
   \fill[white] (O) circle (1);
   \end{tikzpicture}
   \end{document}

To no avail did I try applying \foreach, but this is definitely due to my lack of fluency with TikZ (I always ended up with one color, or at most two nested circle with different color). Could you be so kind and help me with these? A suggestion how to do this would be even better than the full answer.

Best Answer

You mean something like this:

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[mystyle/.style={circle,draw,fill=none,minimum size=20, line width = 8pt}]
  \foreach \x in {1,3,5,7,9,11,13,15,17,19}
\node [mystyle,  minimum size = \x cm, color =red!70]  (2) at (0, 0) {};
  \foreach \x in {2,4,6,8,10,12,14,16,18, 20}
\node [mystyle,  minimum size = \x cm, color =yellow!50]  (2) at (0, 0) {};
\end{tikzpicture}
\end{document}  

which would give you:

enter image description here

I just made the yellow a bit lighter because, it was bleeding yellow too much :D