Highlighting a row once a parameter has been selected in SSRS - reporting-services

Question

I have a report that has 3 parameters: RaceDate, RaceCourse, SilksColours. The SilksColours parameter is optional.
If the SilksColours parameter is selected I want to highlight the row in my report with the colour yellow, while all the other rows stay white.
Is this possible?

Answer 1

For each TextBox in the row you want to highlight, you need need to set the Background Color property to be expression-based and compare the parameter value to value in the row, something like:
=IIf(Fields!Colour.Value = Parameters!SilksColours.Value, "Yellow", "White")
Edit after comments:
OK, as you've noted there are two questions here.
Parameter with default
You have a requirement to have a multi-value parameter with the ability to specify no value in particular. You can't set up a multi-value to accept NULL values, so you need to add a catch all value to the DataSet. So base the parameter on values similar to the following:
Set a parameter up to use this DataSet and set the Default Value to None:
Now we have a parameter with a default, which will not highlight any rows, so users can just ignore if they want or choose values as required.
There is one minor annoyance here - the user can select None and other values as well, they aren't mutually exclusive, but it should be good enough.
Highlighting rows
Next step is to set the Background Color values for all required TextBoxes. Since multiple colours can be selected, we need to treat multi-value parameters differently from single ones, something like:
=IIf(InStr(Join(Parameters!Colour.Value, ","), Fields!Colour.Value) > 0
, "Yellow"
, "White")
So what we need to do is use the JOIN function to create a string list of selected values, then check if the row value is anywhere in that list. Put it all together to get the following:
The report will load straight away as the parameter has a default value, with no rows highlighted:
Choose one colour and the row is highlighted:
Choose multiple colours to highlight multiple rows:
Hopefully all this is what you're after!