Newsletter  (Nov 2013)  Page(s) 12.  
 
[From "California's oldest surviving roses", by Darrell Schramm]
Sievers went on to produce Improved Rainbow, but apparently the improvement was not obvious, for after several years it vanished from the market.

Book  (2007)  Page(s) 295.  
 
Improved Rainbow (Burbank, c1893). T Spt or sdlg 'Rainbow' (T). Pink str. Red.  

Book  (Jun 1992)  Page(s) 328.  
 
Improved Rainbow Tea. Luther Burbank 1896

Book  (1936)  Page(s) 595.  
 
Rainbow, Improved (tea) Burbank 1910; pink, striped white

Book  (1918)  Page(s) 118.  
 
Improved Rainbow Fair growth and good foliage; distinct color. 

(Courtesy Brent C. Dickerson The Old Rose Advisor Vol 1, 2nd edition, page 168 [ARA18/118] )

Website/Catalog  (1915)  Page(s) 93.  
 
Improved Rainbow. (Sievers, 1895.) Carmine, rose and flesh. Similar to Rainbow, but larger and with the variegation in numerous small flecks instead of broad stripes.

Book  (1906)  Page(s) 75.  
 
4.828. Improved Rainbow, Thé, rose strié blanc

Website/Catalog  (1902)  Page(s) 85.  
 
Improved Rainbow - Is entirely distinct and far superior to Rainbow. The Improved Rainbow is penciled with brightest Gontier color, every petal in every flower and base of petals of a bright amber color, making a very distinct and charming flower.

Website/Catalog  (1900)  Page(s) 5.  
 
The Best Roses for Winter Blooming Indoors

Price, postpaid by Mail, of varieties described below, plants from 3 1/2 inch pots, except where noted, 20 cts. each; 3 for 50 cts.; 7 for $1.00.

Improved Rainbow. Elegant flowers of immense size; bright pink dashed and streaked with cherry red. Magnificent buds. Blooms grandly in pots.

Website/Catalog  (1898)  
 
Improved Rainbow Just what the old 'Rainbow' ought to have been but never was.  The color is a lovely shade of deep coral pink elegantly striped and mottled with intense shining crimson; finely colored at center with rich glowing amber, makes beautiful buds, and the flowers are extra large, very sweet and of greatest depth and substance.  

(Courtesy Brent C. Dickerson The Old Rose Advisor Vol 1, 2nd edition, page 168 [C&Js98] )