Impixel alternative for LAB Colour space

Hello everyone, I've wrote a program for road extraction to find lines in an image and then do some colour segmentation to display the road. I originally did this in RGB colour model, and plotted the Hough lines on the original image and determined the mean colour of the lines for each RGB attribute. I realise I may get better results in LAB colour space but I'm struggling to determine how. Impixel function doesn't work in LAB, correct? This is part of the code for the RGB scheme;

% Find any lines in the image 
lines = houghlines(Grey,theta,rho,P,'FillGap',2,'MinLength',10);

% Plot lines on original image
figure, imshow(I), hold on
P=[];
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');
   % Plot beginnings and ends of lines
   plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
   plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');
   % find average road colour - get all co-ords between endpoints
   [x, y]=bresenham(xy(1,1),xy(1,2),xy(2,1),xy(2,2));
   LineCoOrds{k}=[x, y]; 
   % Get RGB values for these points & their mean for each indivdual line
   P{k} = impixel(I,x,y);
   Meanpix{k}=mean(P{k});
end

I know how to convert to LAB from RGB already

cform2lab = makecform('srgb2lab');
LABimage = applycform(I, cform2lab);

Any help is greatly appreciated

Many thanks!