This cardigan is constructed from at least five different crochet patterns/motifs, a large portion of which were pieced together with the trellis stitch. The sleeves are based on a scarf pattern, which is also used in the upper body of the cardigan.
Following is a rough description how I put this cardigan together. I also used a simple schematic for a summer cardigan such as this below.

You may use any cardigan schematic to determine the shape and size of your cardigan - and feel free to modify.
SLEEVES
Use this scarf pattern to make the suitable length of sleeves.
Make the cuffs for the sleeves using a pattern for a purse.
BACK
Working the hems:
Start with 1 row of Double Crochet.
Use pattern from crocheted Pillow Cover (3 rows in alternating colors).
Working the back from bottom up:
Into the row of dc, work Treble Clusters found in the Scarf Pattern.
Then continue with the Scarf Pattern’s trellis stitch, then Treble Clusters.
A lace edging for a capelet pattern is then used.
Make 7 rows of alternating colors with Parquet Stitch as shown here.
This is now where the armhole begins.
Proceed with Trellis Stitch for suitable length, decreasing to shape the armholes.
FRONT RIGHT SIDE
Working the hems:
Start with 1 row of Double Crochet.
Use pattern from crocheted Pillow Cover (3 rows in alternating colors) (see pattern above).
Working the front from bottom up:
Continue with Trellis Stitch and Treble Clusters found in the Scarf Pattern.
Then use the border of this pattern for a capelet.
Now, use this pattern:
FRONT LEFT SIDE
Same as Front Right Side but done in reverse.
ASSEMBLY
Use sc to assemble.
NECKLINE
Use this pattern for the neck area.
FRONT SEAM AND BUTTONS
Make suitable length of motif of pattern from the lace purse as shown above. Sew along front of cardigan opening.
Crochet small buttons and sew along other side, align with small gap between motifs which serve as button holes.
Weave in all ends.

The back section of the cardigan. Rows of Parquet Stitch in different colors was used to separate the lower and upper sections.







Gorgeous!
I like the color combination with your dress, too. I like bright colors and this has the right balance of brightness and muted tones.