Define a function called plotlines that accepts y as an array of y-coordinates and linecolors as the colors for the lines. The function creates a colored line plot of the values in y.

Within the function, check the validity of linecolors by calling the validatecolor function. Specify the 'multiple' option to allow users to specify one or more colors. If the colors are invalid, validatecolor displays an error message. Otherwise, it returns the equivalent RGB triplet array. Next, use the size of the RGB array to determine the distribution the colors among the lines.

Save the function as plotlines.m in a writable folder.

function plotlines(y,linecolors)
% Plot colored lines.
p = plot(y);

% Check for valid color values
RGB = validatecolor(linecolors,'multiple');

% Use RGB array in a calculation
ncolors = size(RGB,1);
nlines = numel(p);
nupdate = min(ncolors,nlines);
for n = 1:nupdate
    p(n).Color = RGB(n,:);
end

Call the plotlines function to plot a red, a blue, and a black line.

plotlines([0 1 2; 1 2 3],{'red','blue','black'})

Now call the function with an invalid color value. In this case, specify a scalar value instead of an m-by-3 array. MATLAB^® displays the error returned by the validatecolor function.

plotlines([0 1 2; 1 2 3],255)

Error using validatecolor (line 50)
Specify colors as a three-column matrix.

Error in plotlines (line 6)
RGB = validatecolor(linecolors,'multiple');

Define a function called plotminmax that accepts y as an array of y-coordinates and c as an optional color argument. The function creates a line plot with dashed horizontal lines at the minimum and maximum values of y. The dashed lines are black by default, but the user can customize the color with the c argument.

Within the arguments block, check the validity of c with the validatecolor function. Define 'black' as the default color so that c can be an optional input. Then, plot y, and display horizontal lines at the minimum and maximum values using the color c.

Save the function as plotminmax.m in a writable folder.

function plotminmax(y,c)
% Plot lines with horizontal lines indicating min/max of y.
arguments
    y {mustBeNumeric, mustBeNonempty}  
    c {validatecolor} = 'black'
end

plot(y)

% Add min and max lines
ymin = min(y,[],'all');
ymax = max(y, [],'all');
yline(ymin,'--','Color',c)
yline(ymax,'--','Color',c)
end

Call the plotminmax function with the hexadecimal color code for red. The function plots the coordinates and displays the horizontal lines with the specified color.

plotminmax([8.4 2.5 7 3 9.2],'#FF0000')

Call the function with an invalid color value. In this case, specify an invalid color name. MATLAB displays the error returned by the validatecolor function.

plotminmax([8.4 2.5 7 3 9.2],'chartreuse')

Error using plotminmax
Invalid argument at position 2. 'chartreuse' is not a valid 
color specification. Valid names include: 'red', 'green', 
'blue', 'cyan', 'magenta', 'yellow', 'black', and 'white'.
Valid hexadecimal color codes consist of '#' followed by three 
or six hexadecimal digits.