How to customize plot color using xcolor?

Question

I am trying to plot multiple data sources on the same plot and differentiate between them with color. Here is a minimal environment for replicating the errors I am getting.

\documentclass[a4paper,12pt,openany]{book}
\usepackage{xcolor}
\usepackage{pgfplots}
\definecolor{LB1}{RGB}{173,216,230}
\definecolor{LB2}{RGB}{135,206,250}
\definecolor{LB3}{RGB}{0,191,255}
\definecolor{LB4}{RGB}{30,144,255}
\definecolor{LB5}{RGB}{70,130,180}
\definecolor{LB6}{RGB}{123,104,238}
\definecolor{LB7}{RGB}{0,0,255}
\definecolor{LB8}{RGB}{75,0,130}
\definecolor{LB9}{RGB}{138,43,226}
\begin{document}
\begin{figure}[!h]
    \centering
    \begin{tikzpicture}[scale=0.9]
    \begin{axis}[
        legend style={at={(1,1)},anchor=north west},
        xlabel={$x$},
        ylabel={$y$},
        ymajorgrids=true,
        xmajorgrids=true,
        grid style=dashed,
    ]
\addplot[
    color=\color{LB1},
    mark=square,
]
coordinates {(2,3)(6,5)};
\addlegendentry{$r=0.1$}

\end{axis}
\end{tikzpicture}

\end{figure}
\end{document}

I get many errors.

! Missing \endcsname inserted.
! Extra \endcsname.
\pgfutil@colorlet ...g \csname color@#2\endcsname
! Argument of \XC@col@rlet has an extra }.
Runaway argument?
{tikz@color}{@undeclaredcolor }\def \reserved@b {@declaredcolor }\futurelet 

ETC.
! Paragraph ended before \XC@col@rlet was complete.
! Package xcolor Error: Undefined color `\protect \let \reserved@d =[\def \par
! Package xcolor Error: Undefined color `tikz@color'.

How do I fix these errors?

Answer 1

Henri Menke already provided the solution: use color=LB1. But if you want to define your own colors, you can also define a cycle list from where pgfplots will autolatically select the color (and marker) without having to manually fix it.

(Note: You can also take a look at https://tex.stackexchange.com/a/134368/1952 to understand differences between addplot, addplot+[...] and addplot[...].)

\documentclass[a4paper,12pt,openany]{book}
\usepackage{xcolor}
\usepackage{pgfplots}
\definecolor{LB1}{RGB}{173,216,230}
\definecolor{LB2}{RGB}{135,206,250}
\definecolor{LB3}{RGB}{0,191,255}
\definecolor{LB4}{RGB}{30,144,255}
\definecolor{LB5}{RGB}{70,130,180}
\definecolor{LB6}{RGB}{123,104,238}
\definecolor{LB7}{RGB}{0,0,255}
\definecolor{LB8}{RGB}{75,0,130}
\definecolor{LB9}{RGB}{138,43,226}
\pgfplotscreateplotcyclelist{mycolors}{
LB1,every mark/.append style={fill=LB1!80!black},mark=\
LB2,every mark/.append style={fill=LB2!80!black},mark=square\
LB3,every mark/.append style={fill=LB3!80!black},mark=otimes\
LB4,mark=star\
LB5,every mark/.append style={fill=LB5!80!black},mark=diamond\
LB6,densely dashed,every mark/.append style={solid,fill=LB6!80!black},mark=\
LB7,densely dashed,every mark/.append style={LB7,fill=LB7!80!black},mark=square\
LB8,densely dashed,every mark/.append style={LB8,fill=LB8!80!black},mark=square\
LB9,densely dashed,every mark/.append style={solid,fill=LB9},mark=otimes\
}
\begin{document}
\begin{figure}[!h]
    \centering
    \begin{tikzpicture}[scale=0.9]
    \begin{axis}[
        legend style={at={(1,1)},anchor=north west},
        xlabel={$x$},
        ylabel={$y$},
        ymajorgrids=true,
        xmajorgrids=true,
        grid style=dashed,
        cycle list name=mycolors,
    ]
\addplot
coordinates {(0,1)(5,1)};
\addplot
coordinates {(0,2)(5,2)};
\addplot
coordinates {(0,3)(5,3)};
\addplot
coordinates {(0,4)(5,4)};
\addplot
coordinates {(0,5)(5,5)};
\addplot
coordinates {(0,6)(5,6)};
\addplot
coordinates {(0,7)(5,7)};
\addplot
coordinates {(0,8)(5,8)};
\addplot
coordinates {(0,9)(5,9)};
\end{axis}
\end{tikzpicture}

\end{figure}
\end{document}