Good Morning Shadow:
* Good grief !
I sure did write some busy routines. :)
Ahhm, to answer your question.
No.
(looking at Scenario2 source)
I am reading and writing every pixel on the screen, turning it to B&W.
Once it's done, the regular tiles must plot. I could change all the tiles to B&W, but that would be a slow process, and I'd have to copy the original ones to a buffer first if you plan to return the tiles to their original color. GFABasic never was a graphic monster like GBA.
I also see that Scenario2 is a real resource hog.
I was playing WMA XMas music in the background while I program.
When I brought up Scenario2 to check the effect you were talking about, the background music (WMA) starting hiccuping badly.
Hopefully I am programming better than this now !

Now a bit about WMA 9.
This is the standard Microsoft Audio Compression.
It is =VERY= good. Use Sony Soundforge or Microsoft's Free Media Encoder to convert over a Mp3. Use 10% quality and use QUALITY BASE (I know that seems low). Now use an audio editor to compare the two (listen to both). They are =EXACTLY= the same with the slight exception that the WMA sounds more clear (clarity), even though the WMA is 25% the Mp3 size ! Better get converting those Mp3 to WMA gang for your holiday list !

Now with GBA

compared to Scenario2, that's a totally different story. I can already tint the tiles to any color, including B&W (and hold it while you play the game), total fadeout to black, and during all this, maintain original colors for sprites, and add to either, tint, glow, flash, and pulse.
I also have the ability to uniquely color every tile very quickly to any colors, or to return them, but I'm still learning this.
And running the GBA emulator (VGBA) is true 32-bit so it runs very smoothly with anything else tasking it (like WMA playing).
GFABasic does not hiccup tasks if I use GETEVENT instead of PEEKEVENT, but the problem is GETEVENT is about 10x slower at absolute fastest speed.
Scenario4 planned will have GFABasic as the engine (it will use GETEVENT to timeslice), and Basic4GL as the graphic monster (has it's own internal timeslicer so runs well with all tasks).
What is new for Scenario3 ??
Thanks to AXEL, I can now do true ghost effects, like fog that scrolls across the screen, but it's true fog, where you can see the background (not like Scenario2 where there are holes in the fog to show images), but true solid any-colors that merge 50% with background (except frames & text).
Neat stuff !
Scenario3 posted this Monday will probably NOT have the map editor.
It's a devil writing the image-editor since every single pixel is 4-bits and I have to calculate/truncate the values to store correctly in SRAM, and I want to finish this task first.