Adobe Illustrator

Drawing Abstract Lines

Using The Blend Tool

1. Choosing the colors

For convenience, let's choose the colors we are going to use beforehand.

Draw the circles (L) or rectangles (M) filled with light-blue, violet, dark-blue, and the gradient from black to dark-blue as shown in figure 1.

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Fig. 1 Color circles

Move them outside the artboard.

2. Drawing the lines

Pick the Pen Tool (P) or Pencil Tool (N) and draw two lines as shown in figure 2.

I have drawn lines 2 pt wide.

Pick one line to start with. Make sure the stroke color window is active (figure 2). Pick the Eyedropper Tool (I) and click the violet circle while keeping  Shift pressed. This way we painted the line violet.

Fig. 2 Drawing and coloring the lines

Repeat these transformations for the other line except paint it dark-blue.

3. Setting blend options

Open the Blend options dialog: Object/Blend/Blend Options.... Set Spacing: Specified Steps equal to 15.

Fig. 3 Setting Blend options

4. Creating the blend

Select the both lines and press  Alt-Ctrl/Cmd-B or Object/Blend/Make. The result is shown in figure 4.

Fig. 4 Creating the blend and drawing new lines

5. Adding lines

Now draw two more lines as shown in figure 4 and paint them light-blue and dark-blue.

Select them and apply the Blend Tool (Alt-Ctrl/Cmd-B or Object/Blend/Make).

Fig. 5 The blends are ready

5. Adding transparency

Pick the Direct Selection Tool (A) and select the dark-blue line belonging to one of our objects. Set Opacity = 0 on the TRANSPARENCY (Window/Transparency) panel as shown in figure 6.

Fig. 6 Setting line transparency for the line

Now do the same for the line belonging to the second object.

Fig. 7 Transparency is applied

7. Adding the background

Now we can add the background. Draw a rectangle (M) and fill it with the dark-blue to black gradient. We have it ready in one of our circles (figure 1), so one can just click the circle with the eye dropper (I).

Fig. 8 The background is added, the picture is ready!