What is the logic behind illustrators fill and line colour from defaul?
It seems randomly to lurch between black lines or clear lines, between black fills or no fills.
Is there a logic I don't understand?
Well, if i create a new document and start creating squares or lines the first square will for instance be black line no fill but the second will be filled black.
Why? I never touched anything.
Are you creating only squares? Or are you using different tools?
Lines have options. You can choose to apply a fill. See the manual on the line options.
Which appearnace is applied depends on a setting in the manual of the appearance panel: "new art has basic appearance" see manual on this setting as well.
Different tools, its just a inquiry question its not really a bother. I was just creating a very simple set of squares and lines to demonstrate a kitchen layout and could not fathom why it was jumping between no line fill, black line fill, no fills and black fills in squares. Seemed totally random.
Here's a possible scenario, without changing fill or stroke color:
Open a new document. Default settings are White fill, blacks stroke.
Click & draw with Rectangle Tool: White fill, black stroke.
Click & draw with Paint Brush Tool: No fill, black stroke.
Click & draw with Blob Brush Tool: No fill, black stroke.
Click Selection Tool, select Blob Brush drawing: Black fill, no stroke.
Rectangle Tool creates a path with whatever fill and stroke color, if any, are selected .
Paint Brush Tool creates a stroke with whatever stroke color is selected, no fill.
Blob Brush creates a path using stroke color if one is selected, otherwise uses fill color, but shows as stroke color while drawing, then changes to fill color if path is selected.
Confusing, but there is logic.
In other words, the "logic" is that you have to constantly pay attention to what the current fill and stroke settings are, because using a different tool (or selecting a different object) can change that.
And when clicking Swatches to change the color of selected objects, you have to constantly pay attention to whether Fill or Stroke is "in front" (in focus) in Illustrator's silly Fill/Stroke icon.