I think you should be given a choice to do that via linedef flags, rather than that being a constant property...I agree that some liquids shouldn't have white splashes, but water typically should, even when it has a blue colormap.
Anyway...here are some ideas I have for new linedefs:
Linedef Executor: Start Appearing/Disappearing FOF Effect - Basically the same as Linedef Type 64, except it is governed by linedef executors, so it can be started with a trigger. This would make the effect more versatile. This can also resume Appearing/Disappearing FOFs that were stopped with any of the next linedef executors.
Linedef Executor: Stop Appearing/Disappearing FOF Effect (Turn All Off) - If the tagged sectors have an Appearing/Disappearing FOF effect, whether through Linedef Type 64 or through my previous suggestion, all the FOFs are switched off indefinitely.
Linedef Executor: Stop Appearing/Disappearing FOF Effect (Turn All On) - Same as the previous suggestion, except that the FOFs are switched on indefinitely, not off.
Linedef Executor: Stop Appearing/Disappearing FOF Effect (As Is) - Same as the previous suggestion, except that the FOFs are not toggled on or off, and simply remain in whatever state they were in at the time of execution.
Linedef Executor: Change Sector Special - The Sector Specials of a target sector will change to equal a value specified in the linedef's front side texture x-offset.
Linedef Executor: Change Waypoint Sequence - The waypoint sequence of a Zoom Tube or Rope Hang is changed to a value specified by the length of the linedef. I can envision a way to simulate this effect with the linedef executors SRB2 already has, but it would be ludicrously complicated compared to this method.
Instantly Raise Floor On Level Load - At the beginning of the level, the floor of a tagged sector is instantly raised to equal the sector's ceiling height.
Instantly Lower Ceiling On Level Load - At the beginning of the level, the ceiling of a tagged sector is instantly lowered to equal the sector's floor height.
Linedef Executor Trigger: Random (Continuous) - When the Trigger Linedef Executor Sector Special is activated, it will look for all instances of this Linedef Executor Trigger tagged to the sector, as always. But instead of executing all tagged lines, it will randomly select one of them to trigger. Then it will search for another random trigger, and another, and will keep doing it as long as the player is still triggering the executor.
Linedef Executor Trigger: Random (Each Time) - Same as above, but it will take effect only once for each time the player activates the tagged Sector Special.
Linedef Executor Trigger: Random (Each Time) - Same as above, but it will take effect only once.
Linedef Executor: Randomly Execute Linedef Executor Triggers - Similar to the above suggestions, but in this case, a Linedef Executor randomly chooses instances of tagged Linedef Executor Triggers. This might actually be a lot more flexible than the previous suggestion.