Got this from a website (http://weddings.weddingchannel.com/wedding-planning-ideas...:
Morning Wedding
Think "special clothes". Depending on the season, your attire is likely to be lighter colored and a bit more casual that you might wear for an evening wedding. Men should still plan to wear a suit or nice sports coat and slacks, and a tie. Women can wear a nice dress, skirt or suit, and might opt for something comparatively colorful, or floral.
Afternoon Wedding
Dress essentially as you would for a Morning Wedding.
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....and this from another (http://fashion.about.com/cs/tipsadvice/a/weddingguest.htm)
Don't wear white because it competes with the bride. There are plenty of other colors available.
Don't wear black or sequins during the daytime.
Don't worry about wearing the same colors as the bridesmaids or mothers. You can't possibly coordinate with everyone in the wedding party.
Do wear something feminine and appropriate, out of respect for your hosts. Clubwear, overtly sexy clothing (strapless, see-through, etc) doesn't belong at a wedding. If you have to ask if it's appropriate, it probably isn't.
Don't wear opera-length gloves (to top of arm) with anything but sleeveless or strapless gowns.
Do take off gloves to eat or drink.
Do use good judgment if the invitation doesn't specify the formality of the event. A pastel suit or soft floral dress for daytime or a little black dress for evening (after 6 p.m.) will take you almost anywhere.
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Sooooo....I don't think black in the morning is the ideal way to go. If you MUST wear black, as this is short notice to get anything else, pick the least formal looking of the black dresses you have. Try to "casual" it down a bit, with colorful accents so it doesn't look "too evening" (i.e. cocktail-y or sequins!). If you have a black dress with a different trim...pick that O.!
Have fun!