Question

natural sources that can be used as acid-
base indicators

Answer 1

PLANTS YOU CAN USE TO TEST PH 
Beets A extremely essential arrangement (high pH) will change the shade of beets or beet juice from red to purple. 
'Dark' Berries Blackberries, dark currants, and dark raspberries change from red in an acidic situation to blue or violet in an essential domain. 
Blueberries Blueberries are blue around pH 2.8-3.2, yet turn red as the arrangement turns out to be considerably more acidic. 
Carrots 
Fruits 
Fruits and their juice are red in an acidic arrangement, yet hand blue to purple over an essential arrangement. 
Curry Powder Curry contains the shade curcumin, which changes from yellow at pH 7.4 to red at pH 8.6. 
Delphinium Petals The anthocyanin delphinin changes from pale blue red in an acidic answer for violet blue in an essential arrangement. 
Geranium Petals Geraniums contain the anthocyanin pelargonin, which changes from orange-red in an acidic answer for blue in an essential arrangement. 
Grapes Red and purple grapes contain various anthocyanins. Blue grapes contain a monoglucoside of malvinidin which changes from dark red in an acidic answer for violet in an essential arrangement. 
Steed Chestnut Leaves 
Splash horse chestnut leaves in liquor to separate the fluorescent color esculin. Esculin is boring at pH 1.5 yet winds up plainly fluorescent blue at pH 2. Get the best impact by sparkling a dark light on the marker. 
Morning Glories Morning glories contain a color named 'eminent blue anthocyanin' which changes from purplish-red at pH 6.6 to blue at pH 7.7. 
Onions are olfactory markers. You don't notice onions in firmly fundamental arrangements. Red onion likewise changes from light red in an acidic answer for green in an essential arrangement. 
Pansy Petals 
Petunia Petals The anthocyanin petunin changes from ruddy purple in an acidic answer for violet in a fundamental arrangement. 
Toxic substance Primrose 
Primula sinensis has orange or blue blooms. The orange blooms contain a blend of pelargonins. The blue blossoms contain malvin, which turns from red to purple as an answer goes from acidic to essential. 
Poppy Petals 
Purple Peonies Peonin changes from rosy purple or fuchsia in an acidic answer for profound purple in essential arrangement. 
Red (Purple) Cabbage Red cabbage contains a blend of shades used to show a wide pH go. 
Red Radish 
Rhubarb 
Rose Petals The oxonium salt of cyanin turns from red to blue in fundamental arrangement. 
Strawberries 
Tea 
Thyme Extract in Alcohol 
Turmeric This zest contains a yellow shade, curcumin, which changes from yellow at pH 7.4 to red at pH 8.6. 
Tulip Petals 
Violet Petals

Answer 2

Indicators are the substances that helps us to identify whether a given substance is acidic /basic/neutral by changing their colours.

Nature can be considered a natural laboratory with so many natural indicators like :

Turmeric Indicator : 
Turmeric indicator helps to identify basic substance by changing the yellow colour to Dark Red.
Turmeric indicator + acid ---- no change in colour.

Beet Root Indicator :
Beet root Indicator +acid ---> Turns to red.
Beet root Indicator + base ---->turns to green colour.

China rose :
Petals of Hibiscus[china rose ] can used to prepare indicator.

China Rose Indicator + acid ---> turns to red.
China rose indicator + base --->  turns to Green 

Red cabbage Indicator :
Red cabbage + base ---> turns to green 
Red cabbage + acid ---> turns to red

Onion Olfactory indicator:
The smell of onion can be removed if onion olfactory indicator is added to base.