Let x be a character vector and suppose you want to know positions$/$indices of all the entries of x that have value magenta. Create a new vector y which gives you all such indices. For example, if

x $=$ c$("$blue$",$ "magenta", "yellow", "green", "cyan", "magenta", "black", "red"$)$

then, printing y should read

y

$[1]26$

For this purpose, you need to create the vector y within the function wheremagenta$().$