Changing color of numbers in stock exchange AE template with expressions
This is probably not the shortest way of doing it, but it's quick and easy:

Make a null layer with a slider
Make a text layer with green text
Link the source text in your text layer to the slider in the null layer.

You should see an expression like this:
thisComp.layer(&quot;slider null&quot;).effect(&quot;Slider Control&quot;)(&quot;Slider&quot;)

Now add an expression to the Opacity control in your text layer. This is going to make the Opacity go to 0 if the slider value is below zero, or 100 if it is zero or above:
if(thisComp.layer(&quot;slider null&quot;).effect(&quot;Slider Control&quot;)(&quot;Slider&quot;)&gt;=0) {100} else {0};


Now duplicate the green text layer

Rename it &quot;red text&quot;

Change the text colour to red

Edit the expression on the red text layer's Opacity control to this:
if(thisComp.layer(&quot;slider null&quot;).effect(&quot;Slider Control&quot;)(&quot;Slider&quot;)&lt;0) {100} else {0};


Now the red text layer should only be visible when the slider value is lower than zero.
Screenshot of the whole thing below:

If you want a leading &quot;+&quot; before the positive values, you could also make an &quot;if/else&quot; statement in the green Source text control, so you only see a &quot;+&quot; when the value is above zero - something like this:
if(thisComp.layer(&quot;slider null&quot;).effect(&quot;Slider Control&quot;)(&quot;Slider&quot;)&gt;0) {&quot;+&quot; + thisComp.layer(&quot;slider null&quot;).effect(&quot;Slider Control&quot;)(&quot;Slider&quot;)} else {thisComp.layer(&quot;slider null&quot;).effect(&quot;Slider Control&quot;)(&quot;Slider&quot;)};