Niagara color picker user parameter preview no longer updates until confirmation

Starting with UE 5.4, the Color Picker Tool no longer updates preview values in real time for certain editor windows like Niagara when working with User Parameters.

This behavior is a regression from UE 5.2.1 and 5.3, where interactive color changes were reflected immediately in the preview, particularly in contexts like the Niagara System Editor.

I have been able to reproduce this issue in 5.4 and 5.5 launcher release versions aswell as Main stream (from Perforce) using CL 41706997.

Technical Cause:
The issue seems caused by a change in UE 5.4, where SNiagaraColorParameterEditor was replaced with the modular SNiagaraColorEditor widget. In this refactor (see NiagaraColorTypeEditorUtilities.cpp), the new implementation dropped support for certain SColorPickerArgs bindings that previously enabled interactive updates, specifically OnInteractivePickBegin and OnInteractivePickEnd.

Without these bindings, color changes made through bound user parameters no longer reflect immediately when interacting with the color picke which adds extra steps for artists trying to iterate quickly.

A workaround was shared with the licensee who reported this issue through the attached Epic Pro Support case.

1. Create a blank project in UE 5.4, 5.5 or Main (CL 41706997).
2. Add a Niagara System based on the BlowingParticles emitter template.
3. Create a new User Parameter of type Linear Color.
4. In the Niagara System Editor: select the BlowingParticles emitter.
5. In the Details panel, find the Point Attributes > Color property.
6. Click the dropdown icon and choose: Link Inputs → User → select the created User Parameter.
7. Open the Color Picker for the User Parameter.
8. Change the color using the picker without clicking OK.
9. Observe the particle color in the viewport.

Expected Result:
The particles should update in real time as the user changes the color in the picker.

Actual Result:
The particle color does not update until the user confirms the change by clicking OK. It's also worth noting that clicking on the modal (X) button updates the parameter color.

A repro project demonstrating this behavior is attached.