Try this, where I change several properties. There are lots more things you can tweak individually, just click the "See all properties" link in the command window to see a list of them.
X = 1 : 20;
Y = rand(1, 20);
subplot(2, 2, [1 3]);
hold on
plot(X, Y, 'gs-');
grid on;
xlabel('UTM Easting (m)');
ylabel('UTM Northing (m)');
% Get handle to current axes.
ax = gca
% This sets background color to black
ax.Color = 'k'
ax.YColor = 'r';
darkGreen = [0, 0.6, 0];
ax.XColor = darkGreen;
ax.GridColor = 'y';
ax.GridAlpha = 0.9;
ax.FontSize = 15;
ax.FontWeight = 'bold';
hold off
