Hi @Radish_G,
I hope you are well! 
Firstly, I'm not a fan of filtering solely by "Duct Systems" as they honestly do not work the way you want it to in filters and your defined criteria under your filtering options is limited and you have less control over individual elements. I'm going to divert you to THIS POST which goes through what I'm going to show below in a bit more detail.
Option 1: (Filtering different Duct Systems)
I have control over the System Type Colors, the flex duct colors and insulation colors. There is a lot more that can be done by means of not filtering via "Duct Systems". The same goes for Piping Systems...
Option 2: (If you want a quick way to "color code" each duct system individually, rather use System Color Schemes)
I hope this helps!
Hi @Radish_G,
Yes, projects have been keeping me busy over the past few months 
I'll try to answer your question and hopefully I make sense.
Duct Systems aren't physical elements, merely entities in Revit which helps Revit and the user to understand which elements belong to a certain "group/system" within the project. Because of this, the fact that they aren't physical elements, a proper color filter can't be assigned to them. A Duct or Fitting is a physical element which can have a color assigned to it. It has a physical appearance/material type in real life and a Duct System does not. Think of Radio Frequency (or Waves), they are non-physical elements, but they are there and serve a purpose as a communication method between two similar devices for example.
You have 3x options to control the color per "SYSTEM TYPE":
- By means of Filters, as per my first post, the second image. There you need to select the physical elements which you wish to assign a color to. (Best option for me, most control over visual display).
- By means of using the DUCT/PIPING SYSTEM TYPE PROPERTIES and Graphic Overrides. (Images below, not my favorite option as there are other graphical limitations).
- By means of using System Color Schemes. (As per my first post, not ideal as you have the least control over lines).
This image below depicts how Ducts Systems can't have a color when only trying to filter it as it is a non-physical entity:
Lastly, to answer your question about filtering Mechanical Equipment. Remember, there can be multiple system types coming out of one mechanical equipment instance. I normally create a filter for mechanical equipment so that all of my equipment is the same throughout a project. Regardless if there is only one system type or 5 coming out of it. Have a look at my first post which illustrates this. (You have a Supply Air and Return Air System Type coming out of the Water Source Heat Pump and there is also Piping Systems which need to be connected to the Mechanical Equipment).
I hope this makes sense and helps!
Hi @rudi.roux,
Glad to see your reply. And so sorry for the late reply.
But, I wish to say one thing very clear "My intention of filtering is not to color the elements. I want to show/hide those elements of a particular system type."
For e.g.,
I got two system types,
1. Supply Air Duct-1
2. Supply Air Duct-2
But, both system types, classification is same, which is "Supply Air"
Now, I want hide the system type 1 which is "Supply Air Duct-1"
Please take note, each system got variety of elements, which includes mechanical equipment as well.
Following screenshot for your review, also attached the sample project file for your review.
Do you got any workaround to achieve this?
Hi @Radish_G,
What you could do and as far as I'm aware to achieve what you are looking for is to assign a dummy parameter which points to your family categories of your choice or as I outlined in the images below. This will then enable you to achieve what you are looking for. I prefer to use Shared Parameters as they are more flexible. In the outlined samples below and in the attached "Revised Sample Project" I used a Project Parameter. (Which will also result in achieving your end result).
I'm not sure how big your project is or how many systems you have in them. To achieve this, you would need to "TAB" each system type until all elements is selected, then assign that system type name to the newly created parameter which points to multiple selected categories.
Then a filter needs to be created and you will "FILTER BY" the newly created parameter which will point to the same categories.
The images below will elaborate what I'm stating above in further detail.
I hope this makes sense and resolves your issue. This would be the only way I know of to achieve what you are after.
