In fact, every Atari 2600 game is a copper effect. The 2600's graphics chip is one-dimensional, working with only one scanline at a time. To display a picture, the software must run in lockstep as the electron beam traces down the screen, changing sprite bitmaps and colors and positions each scanline as appropriate. In other words, the 2600 literally uses the phosphor on the physical TV screen as the frame buffer. No surprise that this was tricky to emulate, and why 2600 emulators took longer to reach usable compatibility levels than emulators for the later more powerful Nintendo systems.
This was used on the BBC Master enhanced version of Elite (and some other games or the era) to get a best-of-both-worlds choice of the Beeb's display modes. The bottom third of the screen was in mode 2 (low res, 4 bit colour depth (well, 3 bit plus flash-or-not)) to get the higher colour variation for the control displays and the top two thirds were in mode 1 (twice the resolution but only 2-bit colour depth) to get the higher resolution for the wireframe graphics.
However there was another very useful trick to changing colours wrt sync. Basically you wanted to have all the gfx drawing done before the vertical retrace (which is quite a bit longer than the horizontal one), then flip the buffer (during) so you'd get a flickerless display at full framerate. Now if you'd change palette colour 0 (background, including screen edges) to red right after the flip, and then back to black again after your drawing routines are done and you begin waiting for the vsync again, you got to see the top of your screen's background red, up until some percentage of the screen height.
This was basically your performance meter. Code more complex routines and the red area becomes bigger. Add even more calculations, it gets to the bottom of the screen, and when it gets too far you won't be done calculating before the next vsync and your framerate drops to half.
Some times I even micro-optimized bits of assembly code by marking the position with pencil on a post-it on the side of the monitor to see if switching around some instructions would make it go up or down a few millimeters :) It really was that stable (given you did exactly the same calculations every frame--which is often the case for demos, but probably not for games). That is, until Windows came along: multitasking meant you were going to miss that vsync every once in a while and the red bar jumping up and down like crazy.