One approach —
x = 0:0.1:10;
y = exp(-(x-5).^2);
figure
plot(x, y)
hold on
plot(xlim, [0 0]+min(ylim), 'g')
hold off
Ax = gca;
xt = Ax.XTick;
xtv = compose('%.0f',xt);
Ax.XAxis.Visible = 'off';
text(xt,zeros(size(xt)), xtv, 'Color','r', 'Horiz','center', 'Vert','top')
This turns the x-axis visibility off, draws the x-axis in green, and plots the tick values in red. The ticks themselves are also now invisible, they would have to be added back with a plot call if desired.
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