The Fill tool is often used in a wide variety of projects. However, it does happen that the tool does not seem to work as expected. Unless you have a corrupt program (which is quite rare), there is usually a logical explanation and solution. Let's have a look at different reasons why the Fill tool might seem to misbehave.
Is the layer visible?
When working with multiple layers, we often order them, hide them, unhide them, etc. Are you working on the correct layer? Is that layer visible or hidden? Obviously, if it is hidden, you won't see the result of the Fill, even though it is there. Check out the visibility icon beside the active layer to see if it is hidden or visible.
Is the layer covered by something else?
Assuming that the layer is visible, is it the active layer? It is common to try to apply an effect to a layer, while a different one is active. Usually, it will show on the active layer, even though it is not the one you expect, but occasionally, you might have a visible layer on top of the active layer. In this case, the Fill will be applied to the layer, as expected, but it will just be covered by something else. Check what is on the layers above the active layer. It might just be hiding below.
Do you have a selection?
Whenever you have a selection, the effect you want to apply or the tool you want to use will be limited to that area. If you try to fill an area that is not selected, nothing will show. Make sure you use you click inside the selection.
Occasionally, the selection could have been created accidentally and is tiny. In that case, you don't see it, even though it is there. To remove any unwanted selection, go to Selection > Select none (or Ctrl-D). After that, the Fill tool should "work".
Do you have a texture applied?
Even if you have a solid color as a material, it is possible that you have a texture applied to it. Remember that "black will block" so if you happen to have a very dark texture applied, the resulting pattern will be very faint. Check the Materials Properties dialog window to see if the Texture is applied. It is here for older versions of PaintShop Pro or if you are using the Classic palette.
And for the newer versions.
What is the Match mode?
One setting for the Fill tool is the Match mode. This determines where the Fill command will apply. This is similar to the Magic Wand, which will select various pixels based on Opacity, RGB color, or other settings.
Let's start with this image:
If I click on one of the tiles with the Match mode set to RGB Color, it will cover this area:
However, if I set it to Color, it will cover a different area:
Most often, you will not want to fill directly on the layer where there is an image or a design, so you might think that this won't apply to you (unless you have the incorrect layer active), so check out the next possible issue.
Typically, I keep the Match mode set to None and it seems to be
Is it using all layers?
There is one setting that seems insignificant but can seriously affect the behavior of the Fill tool. It has a little checkbox and is called "Use all layers".
When this setting is checked, the Fill tool will consider all the visible layers on your image so it will select the areas to cover based on the Match mode you have chosen. So, if you have a selection to fill and the Fill tool is "spotty", it is likely due to a combination of the Match mode being set to something other than None AND the "Use all layers" being checked.
In older versions of PaintShop Pro, "Use all layers" is called "Sample merged", but it works the same.
What is the opacity?
The Fill tool can fill in different opacity, and that is available in the toolbar.
Although you will typically want to keep it at 100%, there is a possibility that you have accidentally changed it. It is also possible that you ran a script that used a different level. If that is the case, the last used setting will still be set.
Do you want more information on how you can use the Flood Fill tool effectively? Check out this article.