To make the main subject glow, I deliberately rendered everything else in monochrome and with lower intensity. The stained glass window is catching the afternoon light and is the main source of illumination.
Yes, perhaps I should show reflected color on the walls and steps, but keeping a monochrome contrast to the colors in the window was more important to me than trying for realism in the interior of the stairwell.
The window frame is darker and slightly more intense than the walls to provide strong contrast with the stained glass window. The stair banisters and treads direct the eye towards the window. The ceiling on the upper left intersects the window frame to provide a depth cue.
The flower is a red hibiscus and the vase is a brightly painted Mexican pot. The abstract background behind the vase and pot would be painted on the stained glass, since there are no lead lines.
If this were ever realized in stained glass, the background would probably have to be broken up with shapes that could be easily cut with the associated lead lines. This would anchor the vase to the ground and perhaps indicate background forms behind the flower.
The flower and vase show lead lines, as do the red and green border strips. It could be fun to play more with the lead lines, making them vary in thickness, especially where the form suggests a wider line.
The white highlights around the flower and leaves are a happy accident, due to outlines not quite matching up. I decided they added something subtle to the window, so I left them in.