Solution:

In order to have a standard colorbar for plots generated using PCOLOR you first need to set the same ‘CLim’ property for the axes of each plot before you enable the colorbar for that plot (i.e. by executing the COLORBAR command).

Since the colorbar chooses limits and labels according to the ‘CLim’ property of the associated axes, it is important to create (or recreate) the colorbar after setting the ‘CLim’ property.

For example:
% Plot # 1
figure(1);
a = axes;
C = rand(5); % Random values between 0 and 1 for Plot#1
p = pcolor(C);
set(a, 'CLim', [0 1]); % CLim property is set for figure(1) before colobar
colorbar; % colorbar is set for figure(1)

% Clears the workspace
clear all;
clc;

% Plot # 2
figure(2);
a = axes;
C = .25*rand(5) + .5; % Create random values between .375 and .625 for Plot # 2
p = pcolor(C);
set(a, 'CLim', [0 1]); % CLim property is set for figure(2) before colobar
colorbar; % colorbar is set for figure(2)