I found that this period of time didn't have any drastic changes. You could see the similarities to the early 1760s with hints of the 1770s appearing (particularly in 1769). The trimming seemed to have the most change, although it was still subtle. Most changes are so minute it's difficult to differentiate between an individual preference and an overarching style. There aren't as many extants from this time shown, not because they don't exist, but because most are labeled 1760-69 or 1765-75. It really can be hard to tell.
Closure: Stomacher, Closed fronts begin to appear.
Neckline: Square, some rounding begins (especially with closed fronts)
Skirt opening: Still narrow, around 6"
Waistline: Points and flat bottomed stomachers added to curved bottoms.
Style: Both Sacque backs and English backs seen.
Pleats: Pleats still large, take up shoulder span. Beginning to narrow, particularly at waist of English.
Skirt Pleats: 1/2"+ for English, some Sacques have pleating in front.
Shoulder Span: About 10" before armscye. Neckline begins to raise and narrow slightly.
1 piece, looser fit, end above elbow. Pleats at top of shoulder.
Sleeves: Ruffles shorten and become rounder. Single layer fabrics seen, although triples still common. Cuffs can be pleated or plain.
Style: Gathered and Pleated. Waved and Straight (which is becoming more common).
Edges: Pinked and Trimmed.
Content: Self-fabric, fly-fringe, or lace.
Brocades still very common, prints becoming smaller and less intense, although older fabrics are still being reused. Solid Silk Taffeta, painted silks, and stripes are very common.
Very straight, stiff cone bodice. Wide skirts, over hoops or panniers. Draping the skirts up can be seen. Not quite "Polonaising", but seems to be utilitarian (or copying that style). Front skirt points tucked back to keep out of fire and dirt, or pulled up towards the pocket slits to avoid dirty streets soiling the hem. I also found a great deal of aprons in images (more copying of the pastoral style?).
Met Silk Gown, 1765-70
V&A Silk Brocade Gown, 1765-70
Met Silk Brocade Gown, 1765
Isabella, Viscountess Molyneux by Thomas Gainsborough, 1769.
The Studious Fair, 1765
The Seamstrefs, 1765
Divinity in Danger, 1766
The Canonical Beau, 1768
Statute Hall, 1769
High Life in the Evening, 1769