It's easy as you said.
You create a calculation:
Drag on filter card and set to true.
I'm going to go out on a limb here and guess that you do not have any stability that are equal exactly 218.1587xxxxx
I'm assuming now that when you created your parameter you have data type float instead of integer. If this is a value that's something like 218 or 222 you might want to use integer as your data type and then select a step range bottom of the create/edit parameter dialogue box. If you do not have all values. If there are holes as in, no 219 or 220 or 221 but a 218 and 222 you may just consider using a list instead of a range of values.
Finally you might just need a filter here. If you want look at a single value just use the field Stability3 as a filter. Using the parameter + colouring is valuable for seeing how one compares to the others but its messy and overdoing it if you want to use the parameter to select a single value to apply a filter on.
1) Simply drag your conm field onto the filters shelf.
2) Choose Show All (for now)
3) Right Click the Field while its on the filters shelf and select show
4) In the Top Right of your sheet it should appear. In the top right of the
filter there is a drop down arrow click it.
5) Choose single value dropdown as how you want the user to interact with
If you want the user to see all the conms and to see just one in a red
colour and the rest as a grey (to show how it compares)
1) Create a Parameter
2) Choose String as your Data type
3) Choose list
4) Choose add from field (option the right) - select the Conm Field
5) Create a calculated field (Conm = )
6) Use that field on the colours shelf.
7) Right click the parameter (bottom left corner) and select show parameter