Interesting B+W Effect with Filters

[Vautrin]

So I shot a picture using Rollei Retro 400S (black and white film, enhanced sensitivity to reds).

I used either a yellow or an orange filter.

And the flag in the foreground looks completely strange. That's a german flag, should look like this

Instead looks like it's only two colors and the top stripe came out in the front flag.

The really strange thing is the flag in the background clearly has 3 stripes, but in the real world they were the same colors!

 

[ann]

filters lighten their own color and darken the color oppositie them on the color wheel.Looks like they did that in the foreground flag.